Good sized hermits would be the best bet IMO. Really crabs in general. The elctric blue hermit and halloween hermits I had really seemed to attack my rock and were powerfull...
It would have to be big enough to crush their calcium carbonate tube. Most fish that we commonly keep that eat coral only really go for the exposed fleshy portions, and would not try and bite through what is really a snail shell shaped as a tube. If any fish would, I would guess it would be certain triggers/puffers..
But then any fish that would, would probably not be reef safe. I can't see worrying about vermetids in anything but a reef, as they only irritate coral.
