Sorry to hear about your problem! Makes me upset to hear people are still doing this and causing a problem. I say you go to where their trails are and use a back hoe to dig a huge hole and fill it with some kind of die. Then cover it with a tarp or some kind of cloth and then cover it with folage. When they fall into it they will get the die all over them and they will stand out like a sore thumb!!! I happen to see this done as a prank, it sure was funny to see the people falling into the hole. The hole was filled with water and cover like I said. It probally wouldn't work the way you wanted it too however it really stinks when people just feel they have to do this the wrong way. Good Luck with your situation.

River Rat