When I find a roadkill deer that still has antlers, I just grag the hatchet from under the seat of my pickup and do several quick "chops" around the skull where the antlers are growing - forehead, back of the head, and between the antler and the ears. A couple chops and you can usually pull the antler and the skull section free. You might need to cut some hide that's still attached. Be careful of sharp bone fragments/splinters.
Back home I then usually use a hacksaw or small handsaw to trim the skull fragments away from the crown (base) of the antler. The more "bone" you leave attached to the base of the antler, the more you have to carve into interesting shapes.
Just my humble thoughts to share. Take them as such.
Mikey - yee ol' grumpy blacksmith out in the Hinterlands