I've created a form that I make anyone sign who's going to hunt on my property.
It specs out the date of when they are going to hunt and it's says that I have no liability in the matter. It also lists the phone numbers of myself, the PA State Police, and the PA Game Commission officer.
Of course, that doesn't mean that I can't be sued, but it will help a little bit if things ever get legal.
One reason I also did this was to enable my permitted hunter to tell anyone else they see to 'slag off.' I tell people that I don't expect them to confront anyone, but that if they do, show them the permission slip and ask if they've got one (which they wouldn't).