Educating cache placers would be the bast option, but we could also help avoid this problem if we could obtain the boundaries of these areas and let GPSFun aware of them. Perhaps someone should see if they could find out who to contact. If we could even get a rough map with the property lines, I could digitize them so we could extract coordinates from it.
It's not foolproof, but it's better than hoping someone catches it before it causes problems.
Some of these area are harder to keep track of, like the National Wildlife Refuge, because some caches have been allowed there.