We have 3 cats and had a dog that wouldn't bother them, infact he was afraid of them. He died last year so we got another dog. She is very interested in the cats and will chase them. or the first 3 months the cats wouldn't come out of the basement, but now they come out all the ime and if the dog chases them they just go back into the basement. You might want to make a safe room where the cat can go but the dog can't by installing a cat door. 3 days is definitely too early to tell how the dog is going to do. A few months is more like it. Give it time.