A handful of roofing nails will take care of them 4 wheelers. The tracks will tell you where they are crossing the line and where they are coming from. Visit them and take notice of who is smoking a cigar and has a 4 wheeler.Narrow it down. Let them see you walk around with a assault weapon everywhere you go on the land.Once and a while when they are up at there lease rattle off a couple hundred rounds in to a target.Get one of those human targets and mark tresspasers on it,Fill it up with holes. They will get the message from the lead.Make them think your crazy.When I firs moved here I made sure people seen me with my AK everywhere I went while on the property.I even mowed the lawn with it on my back. They got the message.