Nulle- If you're interested in mounting a fox I would sell you one ($10). I studied a little bit about taxidermy myself, I like to tan furs but I never tried to mount something.
Blktail- I use 1 1/2 to a 1 3/4 duke coilspring and stake them with rebar. This coyote was not too big but the 1 1/2 held him tight (i was trying to catch a fox with that trap).
And I try to clean up all the skulls, but I shoot them with a .22 LR in the head, so sometimes the bottom of the skull is blown out a little.