Tuxedo urchin causing havoc with my frags

[Reef Pilot]

My Tuxedo urchin does a good job of keeping my rocks clean, and so want to keep him. But he really moves around the tank, and occasionally finds his way up to my frag rack. He knocks them over, often right off the rack, and sometimes carries them off, too. So needless to say I have lost a lot of frags due to this urchin.

But like I said, I don't want to get rid of him. Any ideas or tips on how to keep him off the frag rack (plain eggcrate style)?