I think its the smell of dried blood that the squirrels don't like. But after a while I don't smell a thing....its just when it is still fresh that it stinks.
The blood thing worked really well getting rid of some deer that were eating my roses. The only problem I had was it was in powered form and I made the mistake of mixing it in the kitchen sink. I ended up looking like a bad witch from a horror movie and the whole house smelled like....well, you can guess. Good luck.
P.S... I know some people here in the South that would eat them for you. Just an offer.