I think that a lot depends on the way a dog owner arranges things to prepare for another animal, especially a cat, for the arrival of a new dog. If the cat has had the run of the house in the past, it's unlikely that he or she will willingly allow a dog to roam in his or her territory. On the other hand, it's unlikely that a dog will be willing to remain confined to a single room.
The only solution seems to be temporarily confining the cat to its favorite room, making sure that it has a high enough perch to jump on and sit should the dog accidentally wander in that room. And the challenge is magnified if an owner already has three or four indoor cats and is taking in a dog besides. Maybe in this case, it's a good idea to hold off on getting a dog for awhile. Biding one's time is extremely important, as you don't want to rush things too quickly just yet.
The good news is that if you take things one step at a time, the cat(s) and new dog will eventually get along or at least co-exist peacefully. .
Life is hard
2 years ago