Figure out when the local gem and mineral show is around you. Bring your fossil but leave it in the car. Approach any of the guys there that are rocking fossils (there will be many) and tell them you have a Styracosaurus horn, it was found by your father, and you want to be able to show it in a cool way. They'll give you all sorts of suggestions about mounting, polishing, etc. Trade in fossils is nothing like trade in antiquities. Fossil sales are mundane (and rife with forgeries) with very little control. Unless you have strong reason to believe your specimen is archeologically vital, there's no reason not to enjoy it. Me? I'd get one side of it polished and then mount it. There might be some really cool structure you aren't seeing that would really set it off. Again, I'd ask at the lapidary show.