Originally Posted by Benamayer
Yea that's what I meant, not silicone sorry... But I probably shouldn't glue my entire structure together, right? Just a few pieces?
You may not have to do that at all. Just make sure that your bottom rocks are resting on the glass. They can only move sand. When the rock structure is supported by sand they can tumble as the engineer moves the sand around. If the rocks are resting on glass he can move all the sand he likes and the structure will remain sound.
Still, epoxy is great for placing tricky pieces of rock together. It's excellent stuff to have on hand. If you only use a small amount the rocks should be able to be separated with a strong twist outside of the tank if you decide to change things up.