Ideas for clam holder in a barebottom tank?

I've got 2 clams and a scallop and was hoping for a clean way to make a stand for them to keep them upright. No matter how sturdy they look when I leave, they're always tipped over when I come back to the tank. Can I use pottery in my tank? Any other ideas?
If not, I've got a teardrop maxima, derasa, and an electric flame scallop for sale!

 

Let me know if you do end up selling them.

 

Pretty sure they sell these at the swaps.  I think Reef Koi had some for his clams.  Pretty sure these are it  [class="Apple-style-span"]Clam Holder[/class]

 

that looks like it would work perfectly...

 

How about a wad of epoxy with a "dish" shape in it? Although it might not help at all being the clams are gonna lay how they wanna lay.

 

Even though mine are on a sand bottom, I have them sitting in a piece of pvc to keep them upright. Both are actually attatched to pieces now.
Josh

 

Gered, I think I might order some of those clam holders and give them a try.

Jeremy, I thought about using some epoxy and molding them to it, but I'd have to buy the expensive reef safe stuff and I'm afraid that it will form to them if I don't form and dry it ahead of time.

I thought about putting them in my 6 gallon fluval edge, but I think they might be a tad too big.

 

For what it's worth, I don't think there is any difference between regular plumber's epoxy and the "reef safe" stuff besides color.