I use 2 different utensils for skinning a hog. To cut through the skin, I use a utility knife with a roofing hook blade. One hog - one side of the blade. Turn it around and use the other side for another hog, then throw that blade away. For separating the skin from the meat, I use one of several small bladed knives that I have. None are more than about 3 1/2" long. Short blades work best for skinning.
I switch to a longer bladed knife for the actual butchering.