I would recommend letting the foot grab onto something then gluing that to where u want it. That's what I did. Clam is happy it's been a few years since doing this still happy calm.
I did with mine. But you glue the sell not the meat, and glue one side of the sell only.
With crocea clam, they will attach themselves to the rock eventually
Get some wedding vale and a ceramic frag disk for clams. Rubber band the vale over the clam. Give it space to open its mantle. No need to glue the bottom of your tank. I mean I guess if you want... dont get glue on the foot.