Does the cat have a safe place to go to? A place where the dog can't follow. For instance, you could try putting a baby gate in the door of one room and either raising it enough so the cat can get under it or show the cat that he/she can jump over it and the dog won't follow. I think that might cut down on the chasing because when the cat is sick of it, they could escape to their room. I don't know if this is feasible in your set up but it might be worth a shot. Good luck!