Franklin my normally perfect little boy has become quite the terror. I don't know what to do about him! Ok, he is actually still wonderful 99.9% of the time, but HE IS CHASING MY CATS! I had the cats before I had him, I have 2 of them and he was raised to respect them and not chase or torment them. Since re-homing Kirby, Franklin has made it his personal mission to make the cats lives a living hell. They aren't allowed to walk down the stairs or into the living room without him chasing them back upstairs or out the dog door, in the middle of the night if a cat meows when coming into my room Franklin is after it like a shot. It really has become very annoying for both me and the cats. I tell him no, I tell him leave it, I tell him quit but usually by the time the words are out of my mouth the chase is done. If I see a cat coming I can tell him to leave it and he won't go after it but I am not watching 24/7 for a cat to walk in the room. At this point I just don't know what to do! He has NEVER behaved this way and I really would like the kitty torture to stop.  Any suggestions?

UPDATE: after close observation today I think I may have found a part of the problem. One kitty is egging Franklin on while the other kitty wants nothing to do with him! The strange thing is, Franklin doesn't chase the kitty that is egging him on as much as he chases the other cat. Should I still go with the old course of action of not allowing him to chase the cat at all since one of the cats is clearly suffering? Is it reasonable to expect him not to chase cats if one cat is teasing him? Franklin is a doggie genius so I do think it may be possible for him to learn its ok to chase the crazy cat but not the nice cat, what do you guys think? I would rather have him chase nobody, but just wondering if this is possible with one cat clearly asking for trouble.