In my story I've got a shop called "Don's Bait Shop" or "Don's" for short. If I then want to describe something belonging to "Don's" do I have to add a further possessive? For example, if I were to use, say, Wal-Mart: "Wal-Mart's floors were covered in filth." I added the possessive. If I then replace "Wal-Mart" with "Don's" I get: "Don's's floors were covered in filth." But the extra possessive just seems silly. I suppose I can choose how I want to do it, but what is the official ruling?