I think they actually roped off the area every year for a day. I guess if I ever got into a situation where effective encroachment was happening, I'd be asking the county why they aren't charging the encroacher property tax for the taken land...
that would be a very effective technique.
The key is that the landowner has to make it clear that any USE of the land is permissive, and not by PRESCRIPTION, in other words, the user is not establishing a claim by prescription (adverse).