No tractor, no drag where I work, so the arena doesn't actually get dragged. Fortunately it's never been much of an issue, although, since they are smaller arenas, any bad parts are raked by hand when needed. The indoor gets watered usually every other day, maybe every 3 days depending on how dry the air is. Right now the humidity is higher so it stays damp a little longer. The outdoor doesn't get watered at all.

eta: They are picked out after every ride.  If you are working a horse and it goes, you pick it up before you leave.