Private property. That's all they need to tell the kid and the parents. You were on my property, you were touching my sign (or whatever else), you paid a price for it.

The kid and the dad should be happy it was only hooked up to an electric dog fencing system. It could have been much worse.

The guy who did it should also post something to cover his butt though, as well. "Touch at own risk" or something. Cover your butt is the motto today in this lawsuit happy society.