Get a sprotdog 1800 electric shock collar, charge up the battery set it to the highest level place collar on dogs neck, wait for dog to go for cats hit the juice button hard let it burn in. After a few of these that dog will leave the cats alone. In a dog fight however it will keep them fighting as the shocked dog thinks the other dog is doing that to him so be carefull.
18 month Rotti/Shepherd mix will not be much of a bird dog, good luck on that.
In a dog to dog fight, I grab a set of legs and swing em around awhile, they soon learn to stop the fighting. I got 6 GSPs and they all work together or they get a swing.