Your perimeter should give you standoff from bombs if that is a real risk, any in any event must block lines of sight in and allow lines of sight out, let you get in and out, and slow intruders down in and out. As for preppers, the risk is not so much vandalism or violence as theft. If explosives are going to be used it will probably be as a method of entry, which would have to be addressed with a bunker. You still need reaction time, so the further the perimeter from the building the better. Ideally, you will have a clear zone of twenty feet outside the perimeter and fifty feet inside it with no structures or hiding places, or at least the US DoD arms standard of twelve feet outside and thirty feet inside.
Do not panic if you cannot get the standoff you want. You may have to close the road, move home or accept the risk like GCQH do in their town centre annexes, where, instead of armed response cars, standoff and anti terror fences, they have a G4S guard on minimum wage come out to see you with no backup through an open door straight onto the street.
Patrols are to deter, detect and react. They may also check everything is locked and monitor CCTV and alarms.
If you have an estate of over a square mile you should have a perimeter road which you can drive around for inspections. A fence may be impractical, in which case you should consider patrols, alarms and drones.
After SHTF you may want to seal off your estate, road or neighbourhood so would need patrols to also run the gate.
Try not to use single man patrols after dark. Make patrol times random.
Ideally you share a quick response force through your mutual support group to backup your patrol.
It is British tradition that guards shout a warning unless it would endanger them and even then do not shoot to kill.
Fencing is usually the first layer of your defence-in-depth concentric rings, forcing adversaries to overcome different types of obstacle. If the intruder is not deterred by the approach to your boundary then your boundary had better be good. Generally you want to buy time to react, to see someone coming and to make it hard to pose a danger to your building. Your perimeter is key to lengthening the aggressor sequence, otherwise the adversary starts the clock at your facade.
Fencing is usually also, or anyway supposed to be, the outermost defence layer (at which point you get at least enough reaction time). In theory, you could have additional defences beyond that to mark the perimeter, but extra fences are rarely worthwhile unless alarmed and may simply tip off the value of the site. If you want an extra fence to mark the boundary then use 4’ high barbed wire. Beware pushing your only fence out too far as then you have to surveil and maybe patrol it all.
Fencing only slows down attackers by seconds and forces them to be seen or heave objects over the top, but sometimes that is so important that it is worth making it so strong that attackers give up or go over the top or take so long that you can react. Hence there are extremely strong fences designed to only last a minute to stop you being rushed. Ultimately your fence may need only be the toughest in the neighbourhood, not the world. If somebody wants over your fence, they need only spend enough money on a ladder.
In reality the purpose of a fence is to deter by painting a line of demarcation beyond which intruders may be challenged, and to detect by acting as a structure to which to attach alarms. It also serves to deter by worrying intruders that they might not be able to get back our the way they came in quickly enough, to keep guard dogs in and to channel intruders towards gates that you can focus on.
Fences are really part of a system with alarms, lights and surveillance, without which only the most casual intruder will be put off.
Henriksen sell not only carbon pole ladders with hooks, but rope ladder launchers.
ResQMax sell VerTmax 50’ telescopic urban pole delivered rope hook ladders and ALM rope ladder cannons.
The fence is not there to stop a determined intruder, but rather to give you something to mount alarm sensors on, and prove you were entitled to shoot them once they land. Fences are not to stop intruders getting in, but to give guards time to react. Military security designers assume an intruder will vault a chain link fence in 4s or cut it in 10s. Who will your guards be?
Unfortunately, in urban areas you don’t have the physical depth for good security such as see-through fences and perimeter alarms, although you can often reinforce vulnerable spots with spikes, and alarm, light and film them.
If you have the space, and aesthetics is not important, then you could set up a no-mans land, with two or three fences, and pile several rows of barbed wire between them 2m high and 3m wide.
Normally cost, aesthetics, open front gardens and space means homes do not, or even cannot, have a worthwhile perimeter and so should spend the money hardening the building and/or on a saferoom.
Perimeters need the support of CCTV, alarms and lighting for verification and tracking, which will need battery or solar backup for SHTF.
High security applications use sensor cables attached to the fence to detect shaking or cutting, but these need expensive controls, software and monitoring teams. Such installations also sink the fence into concrete foundations to stop it being lifted or tunnelled. Well funded institutions sometimes use radar for tracking post-perimeter breach, or for drones.
After SHTF, you might take the view that intruders will probably not have vehicles or power tools due to lack of fuel, and will not want to lug demolition tools far either, suggesting you could just plan for hand tools no worse than a club hammer and boltcutters that would slip under a jacket. On the other hand, if you think state actors will target you for confiscation etc then you need countermeasures to tactical gear like Blackhawk DETFC fence climber footholds (£210 to import), or Tac-Up’s Tac Flap which covers sharp toppings or Tac Fence Step which is a bracket rung for vertical bars, or Tac Ladder Hooks which can stick into the top of a collapsible ladder.
Round the back you are probably wanting to prevent penetration or climbing over a fence or gate, whereas out front you are probably trying to stop vehicles ramming you, and making the approach witnessed, recorded, detected and lit.
RISC Authority have a video on vacant site security which is a handy primer if you ignore the squatter section at the end.