paints and sealers water resistant

This is not a tutorial but a question, but didn´t know where to post it.

Hello friends, a friend of mine has asked me to do a figurine that wants to keep underwater, as if it was aquarium decoration. There won´t be any living animal or plant inside the tank. I have no idea which matherials I could use to paint the figurine, and maybe a finishing spray like a sealer or something like that. Do you know what could I use? thank you!

It could be sealed with epoxy resin
http://www.talkcomposites.com/6036/3D-Rocks-for-an-Aquarium-using-polystyrene-and-epoxy-resin

Or applying coat of transparent silicone.

Thank you :)