You'll never get through to such thick heads as that's how the parents were also raised.
In my small town I have a fair chunk of ravine property that I don't do much with as it's a treed ravine but I do leave all the wild black raspberries there for the birds so they won't raid my raspberry patch. Imagine my surprise when one day I found a car load of people picking the berries there. I asked what they were doing and they said they didn't want to see the berries go to waste on un-owned land. Yeah, right. Like free land is ever gonna happen. I informed them that I owned the land and I wanted them out. They left with much grumbling about wasting resources, etc. Since I pay the taxes on that land, it's my resources to waste as I choose, which was to keep the birds out of my food.
That was bad enough, then the next year the strip of property below mine was sold and I found the new owner setting in survey sticks to build his new house on my ravine. Seems the realtor, another ignoramous, told them that it was unclaimed land and they could consider it theirs. So they planned to, until we straightened them out. The bottom strip is up for sale again and this time I think I'll post a sign at the boundary that it's private property