We give our two the starfish. The whole starfish, they take a few weeks to eat it all. Once they get ontop of the starfish.. which is literally seconds from introduction of the star to the tank.. the star doesn't have a chance. It doesn't move, unless they drag it around where they want it to be.

Some harley owners will offer a leg at a time and keep the star elsewhere so it can regrow the legs overtime.
We have thought about trying this but I'm still on the fence about chopping legs off a star. I'm not sure what is worse.. being mutilated than eaten or just eaten alive.
So far the feeding schedule for our two has been one every three weeks, depending on the size of the star. First one was a bit small, it took them three weeks to eat it. I gave them a few days without one because we have asterina stars in the tank they can eat as well. Than we introduced another one, larger, it is over three weeks now and they are still munching on it.
What kind of starfish do you feed? CC's are the cheapest for us to get. Though sometimes hard to come by at the closet LFS. For the messing up rocks/corals thing.. we keep an eye on the starfish and wait until the Harleys grab a hold of it before walking away. It takes less than a few minutes.. for such lil' shrimp they are movers.. it cracks me up.
I understand your concern, they are super cool lil' critters.
