Lunging in an arena makes much more work for you as the yard owner - I would advise you have a round pen and say to people they are not allowed to lunge in the arena.
We have a fab rubber surface and can lunge and loose school as long as we rake over the ruts (rake comes out whenever there are ruts, no matter how caused) - however my horse is too unbalanced and heavy on her forehand for me to consider loose schooling. She would trash the place in about three minutes, so I don't do it as I know how much effort YO puts in to maintain the facilities. When we used to have a sand surface it was lungeing only. When we had the old school (years ago before it was extended into the new school we have now), it was used for everything from riding to turning out.
Oh, and all lungeing must be done on different areas of the school, ie. don't stay in one spot, when you change rein go to a different place in the school. It evens it out then and stops tracks forming.
It's funny as we seem to have many rules for things like this, yet no-one has ever complained or broken them.