I live a few miles from Liberty Mountain and agree there is great riding up there. Technically you are supposed to be a student or on staff to ride. I graduated in 08 and figure I paid for it so ill enjoy it.
The area is heavily used by hikers, runners, mtn bikers and occasional equestrian and ROTC. The deeper trails are less traveled but a lot tighter and therefore more difficult.
Heavy is the head that eats the crayons.