[lochaber]

Just posted in your squirrel thread, but pretty much same thing, I wouldn't worry too much about it deteriorating/affecting water parameters, just chuck it in. When I've come across animal skulls in streams, they have usually been completely coated with algae, (more so then the surrounding rocks) so I'm guessing that will happen in a tank as well.

If you are concerned, I'd coat it with a clear epoxy resin, it will be easier to deal with then silicone, and it will just make the bone look wet/glossy (which won't really matter when it's submerged)