I keep my clams on plastic sandwich containers that I have buried(not visible) in the sand. It allows the clam to get a nice suction on the plastic and it prevents bristle worms from going in the bottom and having a very expensive meal. Clams are very susceptible to bacteria entering through the foot. I have had my one large clam for 5 months now he loves being suctioned on the smooth plastic. It makes it easy when you want to move them. Another thing you can try is getting your clam to attach itself to a the inside of a empty shell. This will also help prevent unwanted visitors in your calms foot.
Not sure if this helps......... But its something you could try
