Since our Universe is made up of diverse people and some love cats and some love dogs, there comes a time when these two different types of people decide to co-exist together.
They are certain they can get along together, but what about their beloved pets? Well, with patience and planning, the cat and dog can learn to become friends. Maybe not best buddies, but can learn to live together, if you are patient enough to follow certain procedures.
First of all, you do not throw the two animals together and hope for the best. That will only create a situation where one or the other will get hurt or you will create a first impression of fear that neither one will ever forget. Once that happens, you will never have a peaceful co-existence no matter how hard you try.
The most important thing to take under consideration is the dog's attitude toward smaller creatures. Does the dog love to chase squirrels and / or other smaller animals? If so, it has developed a prey drive or enjoys the thrill of a chase. This can present problems when introducing a cat, which normally will run from a dog.
If you are not certain of the dog's reaction, take the dog (on a leash) out to where there are some squirrels or smaller dogs. There you can watch the dog's reaction to smaller creatures. If there is only a mild reaction, that is one hurdle conquered.
If the dog has done and killed squirrels and / or cats, forget it. There is no way you will ever be able to have a peaceful co-existence between the two animals. Do not even let that idea enter your mind, because it will not work no matter how hard you try, the desire will always be there to "get the cat."
As your human relationship unfolds and you think it is going to move into a more serious accomplishment, the time to think of bringing the other two members of the group together is now.
Once you have established that the dog is not going to hunt down the cat and have it for lunch.
My feeling is that the couple exchange pet blankets, now this might seem silly, but by bringing over each pet's blanket to the others home and letting the cat / dog smell it, is the first introduction. I would do this several times while you are in the process of determining what you are going to do with your relationship and living situation.
Once it is established that you are going to be together, bring the cat / dog to the place where you are going to be living. Keep the cat in a carrier and the dog on a leash. Watch the reaction between the two, if it is fairly calm, let the dog smell the cat in the carrier (keeping it restrained).
Feed the dog some treasures and if you also give the cat some through the screen. Keep the meeting short and do this for several days until you see that both pets are tolerating each other and seem a bit more relaxed.
In the meantime, keep the cat in a room with its food, water, litter box and toys.
It is suggested by the Hemane Society of the United States that you feed the pets on opposite sides of the door so that they get used to each other.
Other suggestions are:
Animals are just like people, some we like and some we do not, there is no way to know until you try and even with the best of efforts it does not work. What ever you do, do not leave them alone to work it ourselves, the end result could and would be disaster.