I have used something similar to the Suspenz Universal Kayak Locking System. It is two coated braided steel cables with hoops on the ends that go over the bow and stern then wraped around your roof rack or pole and then locked togheher. Just make sure the slack is taken out of the cable so it can not be taken off the boat.

https://www.amazon.com/Suspenz-Universal-Kayak-Locking-System/dp/B008OO6UVM/ref=asc_df_B008OO6UVM/?tag=hyprod-20&linkCode=df0&hvadid=167139952559&hvpos=&hvnetw=g&hvrand=468868446218141811&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021589&hvtargid=pla-309859981135&th=1&psc=1

���I never considered just looping around either end, thanks for the tip Peter.

The cable Peter recommends looks as if it would have trouble holding a recreational kayak (Wood Duck series, for example) since the loops are so small compared to the beam of the boat. It looks fine for sea kayaks.

Keep in mind, too, that all these systems only keep honest people honest. Thieves with good bolt cutters will hardly be slowed down. Same thing for cables going through the carry handle holes. No matter how tough the cable, wood and fiberglass will not stand up to cutting tools, so 2 quick snips throuh the boat will free it and leave the cable behind, adding insult to injury.

You may want to consider insurance, instead. Then, if the worst happens, you can use the payout to finance a whole new boat build.

On the other other hand, people really are pretty honest. In 20 years, I've never had anyone try to take any of my boats, even when they've been sitting up on the racks for several days, unattended.

Laszlo

You dont just loop one end you loop both ends and lock in the middle wrapping the boat with the cable. There are better systems. But why?  We have them and have not locked up the boats. Of course our big long awkward to unload from the top of the truck kayaks are  likely never that easy to conceal like a normal unlocked door pilfered items, lap tops, phones, guns, etc.  We have traveled across the country with unlocked boats on top of the truck and left them in museum, cave tour , restaurant , festival and WalMart parking lots with no problems.

.

However if you really need the lock I recommend the Lasso Security locks.  We use use these when loading the boats on the canoe trailer. Easier to remove.  We only do it when we have to stay in a motel over night.  We also often leave the trailer at launches with the extra boats on board.  Those mostly unlocked but the $$$ boats locked. 

 https://www.amazon.com/Harmony-Lasso-Security-Cable/dp/B004450CQO

 https://lassosecuritycables.com/compare-all-kayak-locks.php

   I bought a coated cable and made some loops from things at the hardware store for cheap, simular to what PeterSchop  mentioned. Mostly I have not used it.

Ralph

   I just made a vynal covered cable with loops at both ends, added a lock and run it behing the hip brace.