Hi Baroness,
Have you tried using plants as a defence...there are certain trees/shrubs like "bar beris" which is quite torny and is very hasd to break, they are also thorny climbers available. You might have to buy bigger plants to get the effect required but its worth a try. There's nothing illegal with planting shrubs/trees in your garden. I've seen it been done before on tv and woked, try going to a big garden center and explain that you are looking for thorny plants/trees/climbers and should be able to help.