There was once a TV public service show bout protecting your stuff from theft. While discussing the virtues of cable locks, the speaker cut through a cable lock one strand at a time with a pair of fingernail clippers. A big heavy duty chain wrapped through the frame and both wheels and locked to something that would require a jackhammer to remove.
A piece of 1 inch hardened tool steel with crossbars welded to the bottom, a lock loop bent into the top and welded shut, and the whole thing sunk in concrete will inconvenience a thief enough that he will probably go look for something easier to steal.
