I have always believed in giving each animal time to adjust - making the time to slowly introduce them to one another.Separate rooms are essential to start with.having cats on one side of door and the dogs on inside, so they can sniff one another etc and see they are there(under the door) but unable to make contact.....over a few weeks, slowly open the door, with supervision and let them get used to one another.If you really care about your animals, and want whats best for them always supervise new arrivals, whether it be dogs, cats, Bunny's or birds etc.If the cats or dogs are stressed you can always use something like Rescue Remedy/or if you see they have had enough - its back to each separate room for them both.With patience you ll find they will soon learn that friendship is not so bad. spend equal time with both your rescues and settled animals.Good luck