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It is possible to make your garden fences and walls a little more difficult to climb by applying a topping of one sort or another. There's no guarantee that such a topping will stop the thief climbing over, especially if the thieves come prepared, but the extra aggravation will buy you a little time and the thief's attempts to remove the topping or climb over it might be heard by you or a neighbour. Take a look at the various suggestions below:
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Timber trellis with thorny climbers
Timber trellis is mentioned first in this section because I believe it to be the most effective climbing deterrent for a domestic fence.
A square shaped timber trellis of 300mm to 600mm in height with battens around 15 - 20mm² can be fixed to the top of a fence to deter climbing, but to be really effective it needs to be used as a support for a prickly shrub. Take a look at the tables in Defensive shrubs and trees for a wide selection of thorny plants. The strength of the trellis ironically lies in its weakness, for it was climbed by an intruder it would collapse under their weight. It is however very important to fix it very securely to the fence panel and or posts so that it can’t just be pulled off. It also needs a firm fixing to carry the weight of a climbing plant, especially if the fence is exposed to wind. The only downside with growing a thorny plant through a trellis structure is what to do when the timber starts to rot, so do use stainless steel or galvanised fixings and make sure you use a timber that has been pressure treated against wood-boring pests and wet and dry rot.
Your alternative to trellis might be to train the plant along plastic coated wires. The wires can be stretched between extension battens that have been fixed to the existing fence posts or wall.
Typical divisional fence
The fence shown below is typical of that seen on a housing development seeking to gain 'Secured by Design' approval from the police. This fencing arrangement starts with a privacy screen and then continues down the garden with a panel and trellis combination. This allows mutual supervision of each other's garden and the opportunity to chat over the fence. If more privacy or security is desired the residents can use the trellis to support a throny shrub or two. The trellis is strong enough to carry a plant, but would break under the weight of an intruder.
Planning permission for plant supports
If your fence panels are the standard 1.8m with a gravel board then the overall height of your fence will be 2m. Any extensions above this height would normally require planning permission, so although you don’t need planning permission for a prickly climbing plant growing above the fence do speak with your local planning authority first as the framing to carry the plant may technically need permission. Different planning authorities may have different interpretations in respect to structures used to support plants. (See The UK Law concerning fences, walls and gates )
Other fence toppings
Barbed wire and razor tape
Although there might be some very special circumstances where the use of barbed wire and or razor tape may be required I would not generally recommend the use of these materials for domestic boundaries. Its appearance is ugly and hostile and if on a fence that borders lands to which the public have access it should only be used at heights above 2.4 metres, which will require planning permission! You’ll also have to put warning signs on the fence or wall warning of the specific danger. You’ll also be surprised at how quickly this stuff can be removed anyway by intruders coming prepared with heavy duty wire cutters and blankets. (See Highways Act 1980 Section 164 in The UK Law concerning fences, walls and gates )
Broken glass set into mortar on top of walls will require signs warning of the specific danger and I would not recommend its use below 2.4m. Frankly, I wouldn’t recommend it anyway as it looks horrible and you run the risk of falling foul of the Occupiers’ Liability Acts should someone get injured. A burglar, a blanket and a hammer can usually put pay to a bit of glass in short order. (See Occupiers’ Liability Act 1984 and Occupiers’ Liability Act 1957 in The UK Law concerning fences, walls and gates and the true story below)
I was casually walking the beat one day when a bin man came running up to me clutching a profusely bleeding wrist. I got out the ‘just-in-case’ bandage and carted him off to hospital for some stitches. He’d cut his wrist as he threw a new black bin bag over a side gate of a house on his round. He hadn’t noticed the glass on top of the gate put there the week before by the householder. The gate was only 2m high and there was no warning sign to indicate the danger. With the help of his trade union he successfully sued the householder for compensation for his injuries.
There are various types including systems with very long angled spikes designed for use around commercial or government buildings and a 15mm high plastic type designed specifically to sit on domestic garden walls and fences. I’ve seen the latter and I think it may be effective against the unprepared opportunist thief. That said, a coat thrown over the top will render it useless. These prickly toppings come in strips that can be nailed, screwed or glued to the top of the fence or wall. You’ll need to check with the local highways authority before you buy it to see at what height they would allow its use if the fence or wall borders the pubic highway or other land to which the pubic have access. It all rather depends on how they interpret its injurious status in respect to the Highways Act. The use of warning signs specific to the product is recommended. (See Highways Act 1980 Section 164 and Occupiers’ Liability Act 1984 and Occupiers’ Liability Act 1957 in The UK Law concerning fences, walls and gates )
Rotating and spinning toppings
There is a large range of rotating toppings, normally used on commercial and government buildings’ fencing systems, gates and walls. They are all intended to create an unstable top to a barrier to deter climbing. They range from non injurious split aluminium through sharp plastic devices that resemble cacti, to simple horizontal spinning tubes. The non injurious types can be fitted at 1.8m and above and the injurious types will probably have to be set above 2.4m. Once again, if you want to use this sort of device on a wall or on top of a gate that abuts the public highway or other land to which the public have access a quick chat with the highways and planning authorities before you start work would be wise. The use of warning signs specific to the product is recommended. (See Highways Act 1980 Section 164 and Occupiers’ Liability Act 1984 and Occupiers’ Liability Act 1957 in The UK Law concerning fences, walls and gates )
The above paragraphs make continuous reference to the use of warning signs. These not only reduce your liability in respect to the Occupiers’ Liability Acts, but will also act as a deterrent in their own right. They should certainly be positioned on the public side of the boundary fence or wall at intervals whereby it can be reasonably expected that a person approaching the fence is going to see one. However, I recommend putting the signs on both sides of fence or wall in the event that you have people working in the garden. The normal interval between the signs is 3m. The signs should give a clear warning specific to the product you are using, such as ‘Danger Anti-climb Spikes’ and should include a diagram of the danger. Black lettering on a yellow background is often used. (See Occupiers’ Liability Act 1984 and Occupiers’ Liability Act 1957 in The UK Law concerning fences, walls and gates )
Anti-climb (non-drying) paint
Anti-climb paint can be purchased from some DIY centres and locksmiths. It’s usually supplied in 1 and 5 litre tins and is available in a few standard colours. It’s used to deter climbing up rainwater pipes and other building features and over walls and roofs. It shouldn’t be used on walls or fences or anything that is less than 2.4m in height as otherwise someone quite innocent could get covered in this dreadful stuff. You must also use it in conjunction with signs that warn of the danger of climbing, which is especially the case where it has been used on a vertical surface that could be used for climbing. It’s probably not a good idea to apply it in autumn if there are a lot of leaves blowing around! (See Occupiers’ Liability Act 1984 and Occupiers’ Liability Act 1957 in The UK Law concerning fences, walls and gates )
No matter how good your boundaries they can be overcome with ease if you leave things around your garden that can be used as steps-ups. The most often used step-ups include: Wheelie bins left behind or in front of the side gate; furniture left in the garden and step ladders. You can put away step ladders and maybe the garden furniture and you can chain up wheelie bins to prevent them from being moved around the garden.
Danger to domestic cats and wildlife
The laws concerning fencing have largely been written to protect humans rather than other animals and so I think it is right to point out that some of the toppings described above may inadvertently cause injury to domestic cats and wildlife. Please consider this point before you top your fences.
During a crime prevention survey the lady of the house told me that until very recently her husband (who worked for a telephone company and knew all about electricity) had experimented with electrified wires on top of his garden fences. “It was high voltage, but low amps mate so it wouldn’t have killed anybody” interrupted the husband. His wife went on to say that he’d eventually taken it all down as she got so upset watching rather dazed pigeons and squirrels falling onto the vegetable plot only to be attacked by her cat who sat there all day waiting for the next victim.