Occupier's liability

Recently I have been considering putting barbed wire at the top of our boundary fence (between our front garden and waste land, away from the public highway) in order to prevent the local kids climbing over it continuously and causing damage to the already old fragile frame. Then I sat back and considered, what if some stupid kid injures themselves?! I would be liable! Where did the law go wrong? Under the Occupier's Liability Act we are liable for anyone who enters our property whether they are invited or trespassers! So basically a burglar can come in and if he injures himself whilst in the property can sue the property owner for personal injury! How does that work then? He shouldn't be there in the first place, he is a trespasser! If in the middle of the night you met face to face with an intruder would you think twice about knocking him out? You aren't even entitled to protect your property unless you use "reasonable" force, how are we supposed to know if they have a gun/knife on them? Should we just let them take our stuff? And what is the definition of reasonable? - The answer to this is that there isn't one within the law, everything is reasonable this and reasonable that, but just what is reasonable? To different people it may be different things in different circumstances! The law is in much need of change, but with "reasonable" being used throughout the legal system nobody can be bothered or just don't want to.

Glad I got that off my chest it has been bothering me for a while now!
Anne