My solution so far has been to maintain speeds in excess of 65 MPH whenever yak is on roof. Yaks do get stolen off cars, I heard of one guy losing his while he and his son ran in to a diner to get coffe and donuts, so it doesn't take long and it does happen. Some people install s/s u-bolts either in the end if you can reach or inside on a bulkhead if there's nothing else to run a cable thru. Bury the Ubolts nuts in epoxy or something or spoil the threads. Probably doesn't take much of a cable to discourage one of these weiners from messing with yr boat, it seems to be mainly a crime of opportunity. I've also run the cable thru the doors and locked it inside the car to discourage them from stealing my racks at the same time.