Actually, security products are our "day job" so we can help people from this forum with advice if need be.
We had a lot of problems with vandalism, theft and poaching when we first took ownership. We have had two attempts to break into our building - one before it was even finished, and therefore didn't have any security devices in place!
We have had to do a number of things to make the site less attractive to unwanted visitors. The first thing we had to do was build and install a better road entrance. We were concerned about people arriving in caravans and parking on the site, so we made a very sturdy sliding barrier out of RSJ, as well as a gate that would keep unwanted foot visitors out. We also had to put a very Colditz like fence along the roadside. This has worked to some extent, although the determined still manage to climb over it.
We have also had to invent a locking device for our roller shutter door - which led to people trying to get in by using tin snips on the side of the building. We have therefore riveted the sides of the building to make this harder to do. We have had the blacksmith make security grilles to go over the skylights on our building. My husband has just made locking brackets to prevent the solar panels going walkies.
Inside the building we have multiple anchor points in the concrete floor, to which we lock the tractor and attachments and a site box with massive chains (16mm link diameter hardened) and locks. A site box on its own can be stolen - a few blokes can lift it into a van - so we'd recommend locking it down.
We don't leave other very nickable tools down there - a few hand tools, and a little camping gaz stove but no chainsaws or brushcutters.
We have installed an alarm in the building that calls our phone when it is triggered. It also has the loudest legal siren installed, and in the words of the police "if it goes off, they WILL leave". It makes you feel physically sick. Unless they come with earplugs they won't be able to tolerate it for more than a few seconds, and even with earplugs they won't manage it for more than a minute - not long enough to defeat the security chains.
The gate is locked with the same huge hardened chain.
Our water tanks are bolted to anchor points on the walls of buildings too. I have a remote wildlife camera which I occasionally train onto the building and entrance - lots of people look but so far no intruders captured on camera. However we are keen to keep up this surveillance.
We think the fact that the site now looks obviously cared-for, that we are known to camp there unpredictably, and that the site is regularly occupied, has helped. We have also enlisted the co-operation of the hunter who controls the pigeons and other vermin for the local farmers - he has a good look, and on occasion has stopped lads with air rifles from shooting things in our wood. We have also kept good relations with the local gypsies, who look out for non-locals doing bad things around our woods. They usually know who is causing bother and "have a word". This keeps the risk of an intrusion by non-local travellers down. A case of beer at Christmas, and any scrap metal we have going spare, those kinds of things all help.
We have had 24 small trees stolen from our hedge - almost certainly by a gardener who wanted a garden hedge, because the canes and guards went too. There are a few open spots on one boundary, but you have to walk a long way from the road to get in, and most youths won't walk that far. We also had two incidents of fly-tipping in our entrance, one of which was traced to a builder doing work on a local property. The Council and Environment Agency got involved and now we have intermittent surveillance cameras on the site, and a sign saying there is surveillance. So far, no more incidents have occurred.
It is important to log rural crime, as it often doesn't get reported. We have built up good relations with the Crime Reduction Officer, and also the local PCSO who is very keen on our work (she is an artist, who is doing the PCSO work to pay the bills). They often pop in for a chat and coffee, and keep a good look-out on the site.
We haven't painted the Ifor Williams pink though.
We expect more incidents, but have made it clear that the site is regularly patrolled, cared-for, people are watching over it all times of day and night, and it is very difficult to get at any of the equipment that might be nickable and saleable. It has cost a lot of money to do all this. We would have preferred to spend this money on wildlife conservation, and other things to benefit the woods. But then again - without security, the other work could not proceed.
Sorry for rambling - just giving you a flavour of what we have done. The summary is
a) Expect intruders
b) Employ three methods of security: personal/community relations, physical security, technical security - all three are valuable
c) Make the place look cared-for and engage other people to keep a weather eye
d) Look at the place from the point of view of a criminal: how long would it take to defeat your measures, and would that be worth it? What tools would they need to carry (bolt-croppers can cut through most 13mm link diameter chains, there are plenty of cordless grinders available)? How would they remove the loot? Is there a market for it?
e) Talk to the local Police - they know what the local crims are doing, what is their MO, and so on.