Whenever I read posts about courses being trashed I feel really lucky. I can't think of a single course near me that is treated so poorly. Though, if I had a private course I would be concerned one about people trashing it, but mostly about liability issues that might come up with strangers on your property.
Yeah, I would think liability would be a big part of it -- that and the likelihood of people to take more personal liberties with illegal activities on a course they know to be private.
Most private course owners are great people who love the sport, and are happy to have anyone they KNOW come out. I think Biscoe's approach is pretty spot on -- post the course and contact info, but don't post directions. That seems like a good gateway to keep only known people playing the place. And for what it's worth, Biscoe's course is well worth the drive -- easily one of the best courses in VA, even with all the cowpies.