Brain and Blasto Placement

They can be set on rocks, just make sure they are secure, and that the tissue isn't rubbing on the rock.
I've had my open brain in the rocks but it definitely does better in the sand due to the conical shape of its skeleton. If you put it in the rocks ensure it will not topple over as this can cause a lot of damage. Blastos do great in the rockwork and this is the only place I've kept them. I epoxy my blastos in place with aquamend from HD.