or why not secure them carpet grippers to the inside of the flap less noticeable and again lightweight !!
still think razor blades would teach them a lesson
just fit a bomb to the mud flaps. doubt they would go missing then, and if they do atleast they wownt turn up on someone elses car
Not sure if serious but a stupid idea.Just fit sheer bolts or something.Sharp edges is just something to get into trouble over when someone goes there, i.e a Police officer that's pulled you up checking the car over or a garage.