my rock had holes in it to begin with... but now,
yes, they can chip away at rocks. thats why, if you have one in a reef tank you can't just block up the holes if its a smasher and hope that it'll just die... they will dig their way out.
mines a little N. something (not wenerrae, its just weird, heh) and he goes through the rock just FINE!!!!
different species have different wants and needs....
O.s digs under rocks
Spearers dig in the substrate
mine likes to be in the rocks
(I'd assume its also affects what they eat, and it reduces competition between the species)