The law, as I understand it does not say you cannot put barbed wire here, broken glass there or man traps anywhere. The applicable law is that if somebody is injured because of your attempts to prevent unauthorised access to your property and the injured party can successfully claim that his access to your property was not illegal (remember, trespass is not a criminal offence- it only becomes so when you request a trespasser to leave and he refuses) under criminal law. You are the guilty party. It might not seem fair, but consider a 10 year old boy, who only wishes to retrieve his football from your garden, but injures himself on your broken glass, put there solely for the purpose to prevent access to your property? Now, I could write reams on this subject but the law, in theory is there to protect the innocent. And however you might view the ten year old attempting to retrieve his football he is not a criminal in this sense. In fact, preventing the boy from retrieving is football could be theft. I understand the feeling on this subject, but if your son came home with his hand torn to shreds because somebody put barbed wire on top of their fence, how would you feel? My view is, come onto my property, accept the consequences. If the law decides my actions were disproportionate to the threat, I would accept my punishment under the law. It is there to protect us all.