What about demolition derbys? I'm surprised the DNR isn't busted those things up left and right!! And those cars are clearly in an off road circumstance, and even being erosive!
What happens if their ORV sticker is properly put on a smooth surface, and the bumper is knocked off? Do they get a ticket if they go get the bumper and explain to the DNR officer that the bumper was attached to the car at the start of the event?