careful with booby traps as that is just as much against the law, and quite easy to prosecute once someone gets injured. But they are knee jerk reaction when you have been wronged, I understand that.
I think you need cameras high in the air getting pictures at the gate, and put out "bait cameras". "bait cameras" are cameras that have no value, don't work, but appear to be quite nice. You then get your cameras High up in the tree with infrared flash pointing down at the bait camera. Your actual cameras need to be pretty well camoflaged, so they aren't shot or vandalized by the person that realized they were on candid camera.
Security patrol if there is people parking at your gate that would allow entry. Expensive, but random security patrol from a third party would get the word out in the area that you mean business. Word spreads fast.