We were at an Indiana State park last week-end and the camper beside us stretched their electric cord from the power pole to their camper, hanging like a cloths line, about waist high. It looked really odd, and wondered about someone crashing into it in the middle of the night.
We were sitting around our campfire when a teen age girl walked right upon the wire, of course, texting on her phone not paying any attention. She stopped soon enough, but then had walk around the wire and cut through our site, right beside the camp fire and where we were sitting. Actually, we just kind of laughed at her for almost crashing into the wire when it finally hit me why they next camper hung the wire in the air. It was to keep people from walking right behind their camper on the gravel, between their camper and the electric pole (about 10 feet) using that space as a pass through to the bath house.
It then made sense. That was the only attemped "trespasser" on OUR property the entire week-end.
My tactic has always been, if the same people cut through several times, I eventually stop them, strike up a friendly conversation (and I mean friendly), but deliberately engage them long enough their passage through my campsite delays their intended plan, long enough they get agitated at me. I'm still friendly as a feather bed floating on calming lake, but they realize real fast, when they use my campsite as their passage way, they are going to get stopped and be forced into a conversation. It only takes about once and they somehow always avoid passing through our site from them on.
There are better and more creative ways of dealing with things than barricades, obnoxious dogs or road blocks that all say ... YOU ARE NOT WELCOME - GO AWAY!