Unfortunately it sounds like you're buying crap live rock. Turbo snails are not going to destroy liverock. They will not eat featherdusters, they will not eat long tufts of algae, they will not eat coralline algae.
If when they pass through an area the rock looks like base it probably was to begin with and they're just cleaning up the undesirable algae coating it.
They can only eat an algae when it's short and very close to the rock. They can't eat long strands or tufts of algae. Coralline is calcerous. They won't eat that either.
Here's was great liverock would look like.
There isn't a single thing on those rocks that I could see a turbo snail actually eating or destroying.
If you're life is disappearing I would look harder at water quality, lighting, or other similar issues.
Good luck.