I have the same problem my dogs love cat food and the cats love dog food. My vet says that cat food is bad for dogs to much fat in it. So what I do is put the cat food on the dryer in the landry room and when I feed the dogs I put them in other room, close the door till they are done eating.

So far it works great except for with my Great Dane, he's so tall that his head comes right up to the dryer and eats the cat food, haven't figure out what to do about him yet except move the food when he's in the house.