It varies according to the age, breed, and temperament of the cat. Make sure they can always access their food, water, litter box and favorite perches without going near the dog. When the dog barks at them or makes ANY attempt to chase or bite, immediately roll him on his back firmly but not violently, get above him and look him in the eyes while you tell him No very sternly but without shouting. Hold him there until he relaxes and rolls his eyes up; and let the cats see you do it. In my experience (with many breeds of dogs and many cats) it will only take a couple of times for the dog to learn that the cats are yours, not his. After that, they can teach him that it's actually the other way around.
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