I think if I use those dzus fasteners they will be more prone to theft as you can visually see they are removable. With magnets you would never know they were removable, and if they were strong magnets, which I plan on getting obviously, it would take a real hard tug to get them off.

 

You can get them in pretty much any length you need. On the fender side there is a piece that you attach that looks like a bar so when you push the dzus fastener in you turn to lock it and it stays put because its spring loaded. Then when you want to take off you make a quarter turn and it pops open. The chances that someone will actually steal them is low. It doesn't matter if you bolt them on or use magnets, if someone wants them bad enough they will get them.