I have a few deer and hog skulls that I 'did' by setting them out on the roof of a small shed. Periodically I would turn them over. They are up high enough where four-legged critters cannot get them, and too close to a tree and couple of dogs for buzzards to get at. They've cleaned up nicely.
I also have a bear, bobcat and beaver skull that I 'did' by "cooking" the meat off of them. I set up a half a 55 gal. drum over a fire pit to heat the water. As they "cooked" I would periodically cut the flesh off. I then put them in a mild bleach solution to turn them white. More work than the 'setting them out method' but quicker. Took a couple of days. 1 day for "cooking" and 1 day for the bleach.
Katherine