An electric fence put up in accordance with local ordinances and laws is probably not going to be seen as a trap, even if it is a deterrent. However boards with screws/nails placed for people to step on them, and the intentionally icing an area to try and cause slip and falls could open one up to a LOT of problems. Even trespassers have some rights generally against intentional concealed traps. Lights on motion sensors, cameras, that sort of stuff is more likely to be less risky, but at the same time I acknowledge peoples comments about the lack of effectiveness. To be honest, theres a reason I dont put anything outside my house to attract attention, it just draws fire without me being able to legally return it. Also in many places even just pointing an unloaded gun at someone, much less one with rock salt rounds, can be cause for charges. Again, please be cautious and before you do anything seriously consider consulting counsel about a course of action, there is unfortunately a lot of ways for people who are trying to protect themselves and their stuff to get in legal trouble these days.