Shooting trespassers is not actually legal. However, the truth of the matter is that if you have any amount of land, you could make the body disappear and that would probably be that.
This is why you place a shot 10 ft directly in front of the ground where the invader is treading.
If the person is stupid enough to continue, it tends to be a self-correcting problem, if you catch my meaning.
If they are purposefully within a purple posted land-area, they are tempting fate, to be sure.
The thermal scope I use saves everything out to video format, so it's all there if I need it for evidence, in defense of our ranch land.