1997 Dodge Caravan Drive belt slips off

Make sure the splash shield is in place that protects that area. If your mechanic has visually inspected your pulley alignment and tensioner tensioner and everything seems ok, no other contamination, put a new tensioner and new belt on and use Mopar parts. That will clear it up, not much to it. Ok Unless a component on the system is siezing up at times. When the belt is off carefully inspect the driving and driven surfaces carefully.