In Texas, when no trespassing is clearly posted in a reasonable fashion the owner or person in control of the property through a properly executed instrument has the right to do what ever they wish to do with the land and any injury is at the risk of the end user. We had land in the hill country by Kerrville and constantly had ATV'ers and poachers using the area. We posted signs around the perimeter that said No Trespassing-this area being treated for unauthorized use. We then put out nail strips on trails, nails through shingling disks, and dug and covered small trenches along main thorough fares. Never caught anybody but found mutiple blood trails and evidence of flat ATV tires-seemed to slow the problem down considerably.
Also opens yourself up to civil liability suit You can't "do whatever you wish". From time to time, there are folks that go to prison for electrifying doors, making setguns, etc. Basicly, if you do anything that could be considered deadly force, you WILL be charged at least with manslaughter if someone dies. Civil liability is a huge issue as well. Trespassers are a PITA, but you can get it even worse if you do the wrong things when dealing with them.