Once again my mother's Prius takes a beating. This time it was backed up into an illegally parked car resulting in a loose rear bumper cover. My dad had already fixed this problem on the driver's side, so less chaos ensued. Bumper cover retainer $18.64: http://www.rockauto.com/catalog/x,carcode,1434449,parttype,690
This is a video on how to fix the rear bumper and retainer of a 2005 Toyota Prius. This same concept applies to all Generation 2 Prius models. I hope this video provides help and insight.