1990 Dodge Caravan Serpentine Belt Problem

During the month of April, 2009 we were out during very heavy rainstorm. We were forced to enter a street from a parking lot where the runoff water was quite strong and deeper than I had thought. Upon entering this area, the serpentine belt came off the pulleys and was washed away. I purchased a new belt and had it installed. I have since had to have the belt reinstalled when I have been out in a heavy shower. I never ran it through moving water or standing water. The belt simply comes off apparently because water gets it wet underneath by spplashing up on that area. Do you know of there is supposed to be a shield or some type of "keeper" that might need to be replaced. I never had this trouble prior to April, 2009.