Metal that can be cut

[AJM]

This will be a little off the wall, and I'm not sure they still sell it, but try and pet store the carries fish supplies. They use to sell these lead strips that you wrap around live plants to help them stay on the bottom.
http://www.amazon.com/Penn-Plax%C2%AE-A ... 853&sr=8-1

I think from a golfing stor you can get lead weight with adhesive, you should be able to remove the adhesive is the size was right.