Have you worked on the leave it command? My male was a little younger then yours and he did the same thing. I have several cats, to this day one of them dislikes Midnite and once he starts hissing it gets Midnite going. The cats pretty much decide everything in the house. Them running also start a commotion, but he knows leave it and that has worked. Now if he is laying down and one of them come to him and rub up against him, he is fine. I have found having him on a leash is the worst thing. A gate to separate them has worked well, because they are still able to smell each other through the gate. Midnite also has a ball in his mouth most of the time which helps him. If he starts to chase one of them I tell him leave it and get your ball, his ball is the most important thing to him and he will take the ball over the cat everytime .
Misty- Samoyed Mix
Tannor- Golden Retriever CGC
Robyn- German Shepherd CGC, TC
Midnite-German Shepherd CGC, TC
Brennan- Golden Retriever CGC