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I tried the putty but found it hard due to the pourous natur of the rock I have. If you want to attach them you can use nylon screws, putty, zip ties, glue or just make sure they are stacked so they don't move. Movement will also depend on your critters. Some like to move rock, like triggers, pencil urchins like to wedg and can move them, some snails will topple smallet rocks.
Yeah watch the trigger fish , mine digs the sand out from under corners of rocks, and large eels that rap around the rocks and swim in an out of the rocks. I also tryed the putty and did'nt have good luck with it.