Carpet beatles in animal skull

Had in infestation a while ago and still find the occasional beatles. I found out a few months ago that they like keratin, I collect bones and have a sheeps skull on my desk. I sat it in a tub of water and what do you know, fat larva float to the surface. I found shed again under the skull and soaked it again, more fat larva appeared. How can I prevent them from nesting there, if that's even possible? I have pets so I can't use any poison.