If somone becomes a total jerk and gets you to ban them from your land but is then able to fly 20 meters over it and drop great Cut-hollow-physics-scripted-noise-light-shiney-bumpmaped-torii of Anoyance from the sky it could be pretty anoying.
Another thing I think might be worth while is on restricted land (group specific?) alow owner(s) to have the right to MOVE anything on their land. So that if the above situation is possible it can make the person causing said greif think twice as you are able to say... put their objects in a deep hard to reach hole which would then cause them to indefinatly have to pay taxes for their bad behavior
