Peppermints usually only eat small ones, but I have heard of them munching down on big ones. I had a peppermint in my tank to help with an aptasia problem and it only would eat the new ones. It was still very helpful, but it didn't replace having to mix up kalk paste and blast the big ones. That is kind of fun though, so no big deal. On a side note, I used to pull out the rocks that I could and use a kitchen tourch to burn them off.
Get this, they would still come back. Prety tough little guys.