I've had terrible luck with clawed critters eating my coral. Cleaner shrimp have poked at my clam mantles, picked at my pink bird nest and eaten eagle eyes. Scarlet hermits have eaten GSP and blue hornets. Red tip hermits have eaten xenia and trumpet coral.
So IME I would not buy the "100 small hermits" and go only with snails.
If the sand bed is your problem look into Nassarius snails, they are carnivorous, but live in the sand bed.