Yeah...they aren't part of a clean up crew for nothing...they are non-stop eaters. I made some of my own "clam" rocks out of agracrete and an old, empty clam shell. I used the clam shell to make the depression and then used a small straw to poke a hole down further. Once they bore in they are very secure and you can put them where you want. I made flat bottom ones for those that go on the sand and put acrylic rods into those I wanted to put higher up in the tank. Takes the clam no time at all to get in tight and I can move the whole rock when necessary and not have to worry about damaging the clam.
Yes, those snails have a tendency to eat the clam from the bottom up. If you have a stable tank without a lot of things dying, I would feed the snail an occasional meal of silversides, shrimp, squid or any piece of ocean fish. I'll occassionally get a fresh piece of saltwater fish from the store, cube it up, freeze it and than put it into one of those grid seaweed clips and rubberband it to a rock and put it on the bottom of the tank. The clean up crew gets a good meal, and all the fish pick on it until it's all gone.
