I have the same problem with our 11wk AB pup and our 8 yr old cat , luckily she spends most of her time outside . When they are in the house together I just hold the pups collar and make him sit and try to redirect him . Usually after a minute or so he gets the message and leaves the cat alone for a bit . On the one occasion he tried " playing " with the cat she nailed him pretty good since she still has her front claws and he has been more wary than before .