If you own the land, you could easily stop him: file a legal action (such as a quiet title action) to get a court declaration that the land is not his and an order that he stop doing this. But you cannot enforce *other* people's rights: you have no legal "standing," or recognized legal interest, in another's land that would let you act. All you can do is, if you know or can find (e.g. at the clerk's office, by looking at the deed for this plot) the owner, is let him/her/it (if a business or governmental unit) know what is happening and hope they will act.