Every charter company supplies a long cable and lock for securing dinks. It is long enough to use at the dock and to lock it to the mother boat at night. Be sure to thread it through the dink motor and the gas can. We rig cans on a fishing line to various parts of the dink that might be vulnerable as an added measure. If anyone tries to untie or cut the line it makes a hell of a noise. More times than not they will just quietly untie an unsecured boat and float off and you will not know until morning that the dink has been hijacked. Locking the dink just makes it more difficult and they move on.