It's true that many dogs and cats can coexist in peace. Here's how to begin the careful process of introducing dogs and cats so they will (hopefully) get along.
Cat and Dog Introductions: Stage One
Your resident dog or cat should be given the advantage at first. When you bring the new pet home, confine that new pet to one room of the home, keeping the door to that room closed. Your other pet can have the run of the rest of the house.
When you are away from the house, it may be best to keep the resident pet away from the closed door where the new pet is staying. This may or may not be reasonable based on your home's setup.
For the first few days, allow each animal to gradually discover the scents and sounds of the other (between the closed door, of course). Reward each pet with praise and treats if he or she reacts with calm curiosity or just neutral behavior. If anyone shows aggression, anxiety or over-excited behavior, immediately remove that animal from the situation. Try to divert his or her attention to something like a toy.
Hopefully, after one or two days of this, each animal will be able to tolerate the presence of the other without overreacting. Be prepared, as this might take longer. Once you are comfortable, move onto the next step.
Cat and Dog Introductions: Stage Two
Now that they have been able to sense, smell and hear one another, it is time to allow them to see each other.
Get a pet gate or baby gate that you can set up in the doorway of the room where the new pet is staying. This works best if you have another human who can help you. That way, each pet is being supervised directly.
Both pets should be a reasonable distance from one another on either side of the door.
Feed treats, praise and gently pet each animal while slowly opening the door (with the gate in place and closed). Do not make a big deal about this, just keep the mood calm and allow each animal to discover the open door from a distance. Again, if either pet becomes vocal, aggressive, anxious or over-excited, immediately remove that animal from the situation and divert his or her attention to something like a toy.
Repeat this exercise several times a day for one or more days. Again, you can move onto the next step when you feel that both pets can see each other without overreacting.
Cat and Dog Introductions: Stage Three
This is much like stage two, except that you now want to let each pet approach the gate. As always, maintain control over each animal. The dog should be on a leash. Lunging towards the gate should be prevented and highly discouraged. If your cat is comfortable with a harness, put him or her on that harness and attach a leash. Otherwise, stay very close to the cat. Do not allow him or her to jump on or over the gate.
Be very careful not to get injured. If your cat is hissing or spitting at the dog and you pick him up, you could easily be bitten or scratched. The cat and dog should not be allowed to touch one another, they should only be permitted to get closer together. If calmness and desirable reactions continue for both pets over one or more days, you are ready to move on to stage four.
Cat and Dog Introductions: Stage Four
In this final stage of introductions, the cat and dog are allowed to be in the same room together while supervised. At this point, the dog should still be on a leash. In general, the cat is at a greater risk of being injured, so he or should probably have an edge here and be able to run away if need be (regardless of whether or not that cat lived in the home first).
Hold brief sessions where both pets are in the same room. Treat their reactions the same as you did in previous steps. Gradually increase the times of these sessions, each time letting the pets get a little closer to each other. This final stage may take the longest, and during this time, the pets should still be separated when left alone.
Long-Term Living Arrangements
In time, you may find that your cat and dog simply learn to tolerate one another. If you are lucky, they will become friends. In some cases, the cat and dog can never be safely left alone together. Use your best judgment in these situations, and remember: better to be safe than sorry!
Regardless of the outcome, be sure that your home is set up to allow the cat to have a dog-free retreat. Your cat's food, water, and litter box should all be permanently kept in an area that the dog cannot access. In addition, you may wish to crate train your dog to help keep things safe while you are gone. As always, make sure your dog has plenty of mental and physical stimulation. Provide plenty of exercise, engaging toys, and proper training for your dog.