I have 3 cats, and now we just got 2 dogs to visit for a while. The cats get the house, the dogs now have the outside pasture to roam, since they scare the cats and the dogs haven't grown up with cats, and vice versa, so not gonna risk anything. I've had a cat co-mingle with small dogs before with not much problem, the cat was more dominant than the stupid yip yap dogs. If you get a dog when he's a puppy or very young and mix him with cats then (especially when the cats are the same size or bigger), I don't think you'll have a problem. To throw a grown dog in with cats when they've never been mingled before I wouldn't do, as their natural instincts may take over, even if they're just playing they can grab the cats and hurt them. Get a young puppy, and should be fine imo.