My dog keeps attacking my cat!!!?

I know they're territorial, because my cat is alpha-male and my dog is alpha-female. But my cat if 15 and my dog is 3. My dog is a german short haired pointer. My cat is a show maine coon. And even though my dog is fairly big, my cat is bigger(Search maine coons, you'll see their huge). Of course my cat is a 1/3 her weight. But my dog takes every chance she can to attack my cat. He holds his own, and she often leaves bleeding, but I'm afraid that soon we won't be able to break it up and she breaks his back or creates some internal injury. She doesn't do this with my other two kittens. And their the same size as the other cat is. How do I stop the fighting before either of my animals have to go to the emergency vet? Again? (It was the dog, had a huge gash from where he had bit her)