Lasso Kayak Security Cable with Combination Lock is available in a choice of models for one-person or two-person sea kayaks. This cable has loops ("lassos") that fit over both ends of your kayak and meet in the middle where the built in lock is. To adjust the length to fit your kayak so it can't be slipped off the end, you simply twist the cable around your kayak and car's roof rack as much as the slack allows. Since you wrap the cable around your roof rack, your kayak is then locked to the rack. You can set the combination to any number of your choice.

Lasso also makes a model called the Kong Cable that has both a key lock and a combination lock.