This is what i did with two plastic kayaks I have. I took a large U bolt drilled two holes thru a bulk head, took a 4" round electric box cover, drilled two matching holes in it, ran the U bold thru the bulkhead, used the metal disc on the back side, put two locking nuts one each leg of the U bolt, booggered the threads, smeared thickened epoxy over the threads and nuts. I then can use a chain or cable around a tree/car/guard rail thru the U bolt opening. If you use a cable (Kryptonite or something) you can run it thru the U bolt, around the roof into the car/truck and padlock the two ends together inside the car/truck. It's not bulletproof but it will slow it down most people. see below .................. B .................. B ................. MB .............. UNNMBUUUU ................. MB U ................. MB U .............. UNNMBUUUU ................. MB .................. B ...................B WHERE U IS THE U BOLT, N IS A LOCKING NUT, M IS THE METAL PLATE, B IS THE BULKHEAD - it seems i can't get the above diagram to line up correctly. :>(