Don’t put in anything that could kill or injury the trespasser. In today’s atmosphere with a rogue DOJ and feral judges, you’d be convicted of attempted murder.
Check your local laws on what to do when “threatened” by trespassers. If the law is “criminal trespass”, such as breaking and entering into one of your buildings, then you have a stronger case of defending against a daytime or night-time burglarly.
Make sure you have a watchdog, or if the environment is right, geese. Put the geese in a fenced in perimeter. I understand that even in Vietnam geese were used as perimeter guards, and they make a loud noise when disturbed.
No landmines, etc. Courts frown upon booby traps and you will go to jail, as well as be sued up the yingyang.
Remember to vote against Chairman Mao Hussein Obama and Comrade Erid Holder in November. A ballot, at the right time, is as good as a bullet.