gunnerman has the best idea for short runs. Just take a long cable lock and run it through a d-ring or drain holes if you boat alone. Depending where you live there is one obvious option, hitchhike. If you're out in the boonies this might not work, but mountain and river folk are very generous about giving rides. I boated 28 times on the Poudre this summer and always left my truck at the put in and a buddy with the boat at take out while I hitchhiked to the truck and rarely waited more than five minutes (granted the Poudre has very good hitchhiking).
"Ski bums need something to do in the summer, and river rats need something to do in the winter." -Old Colorado mountain bum adage