How much better is a locking one? I had a regular car cover (good quality one) with metal eyelets for tying it down with twine/rope. I ran a small chain at each end and locked one side down. I never got around to doing the other end (didn't have a lock the right size) and only used a chain clip. This was for the short time I had it at an outside storage lot.
Of course, someone could still cut if off, etc, but the harder it is, the less likely someone will screw with it.