by building places up off the floor (e.g., ramps, cat trees, walkways, tops of furniture, etc.) where they can retreat. Ideally, make it so the cats can get all around the house without having to go on the floor. Also, consider feeding the cats up off the floor where the dog can't get. As for the litterbox, IMHO that's what cat doors are for (i.e., so there is no need for a litterbox).