Not to beat a dead horse but taking any type of "self-help" measures (barbed wire, trenches, spike strips, etc) makes YOU the bad guy, legally speaking.Your best bet would be to get the local authorities involved and let them take care of it. A trail cam would be a good idea and could def give you some good evidence but i would be worried about the trespassers stealing them since they obviously have no respect for other people's property.