Find a good match
Firstly, it’s important to consider the temperament and personalities of your current pets. If your dog is one who has been allowed to chase squirrels, birds, cats, etc. in the past and has a high prey drive, then trying to have them co-habitat with a feline will not go over well. Also, if your dog has shown aggression towards cats at any point in the past, then it is absolutely too dangerous and you should NOT bring a cat into their life.
Similarly, if your cat has been aggressive towards dogs in the past or very afraid of them, it may cause too much stress in their lives to have a dog move in.
If you have a large dog or one that plays exceptionally rough, do not adopt a kitten. Instead, consider a large, confident adult cat (even better, one who has lived with dogs in the past).
It is also very important to keep in mind that adult or senior cats will have a harder time transitioning to living with a canine. Cats who have a lived a life without dogs will often become so stressed that they will stop eating, become very ill and hide. Seriously consider all options and your cats’ needs before bringing in a dog. This will be extremely difficult for many older cats who have never interacted with a canine.
Try to match complimentary personalities. Do not get a rambunctious dog for a shy cat. Do not match an anxious dog with wild kittens. Search for personalities and dispositions that will go together nicely, rather than be opposite.
MOST IMPORTANTLY** Don’t ever put a dog and cat together and “let them work it out” on their own. This could be extremely catastrophic and end in injury or death.
If your cat(s) are indoor only, clip their nails. This will reduce any damage they may cause when feeling especially threatened or frightened during the initial introduction.
You will also want to take your dog on a long walk or engage in a serious play session so they will be more relaxed when first meeting the cat(s).
For the actual introduction, put your dog on a leash. Do not attempt to do an introduction if your dog is not leash trained. You really will need that extra level of control to keep everyone safe. Place a baby gate (or two stacked on top of one another if your cat can jump over the top) to block two separate rooms and have your cat on the opposite side as the dog.
Sit on the side with your dog on a leash in one hand and treats in the other. Treat and praise your dog every time he focuses on you and not the cat. You can have toys available for distraction too. Clicker training is another great option to look into if you’d like. You will be able to click and treat the dog for a relaxed body posture or to direct his attention towards you.
If your dog gets tense and starts focusing on the cat, divert his attention. When he breaks his stare, click and reward (or praise and reward).
If the dog isn’t comfortable, back up and start as far away as needed to help him relax. As the dog gets more comfortable, you can slowly move closer but just a few inches at a time. Stay at a distance that is comfortable for the animal who is stressed or anxious.
Walk the dog back and forth in front of the baby gate and reward him each time he focuses on you and follows your cues. If he lunges, barks, growls or stops and stares at the cat, walk him away from the baby gate until he relaxes. He will learn quickly that his relaxed and calm behavior will get him closer to the baby gate, but his rambunctious behavior will cause him to leave the area. Do not yell at your dog or jerk at the leash; simply walk him away from the cat area and allow him to calm down and try again. If he becomes reactive, walk away again. He will eventually get the idea that calm behavior is the best option.
During the introduction sessions (it will take multiple), if at any point the dog or cat appears dangerously aggressive, this is not a safe match. If you are unsure, feel free to contact a behavior/training specialist for a second opinion.
During the introductory phase, always keep the dog and cat separate, unless you are there to supervise. Keep the dog on a leash until you are absolutely certain that each animal is comfortable with one another. NEVER leave the cat or dog unsupervised, even if it is only for a few seconds, until you are positive they have established a safe relationship with each other. This process could take days, but more realistically weeks, so be patient and do not rush through it.
There will be some environmental modifications that need to happen once the cat and dog are co-habitating. Make sure the cat has plenty of perches and places to get up high and away from the dog. Plenty of cat beds, hidey-holes, shelves, etc. Have a bed or two for the dog that he can always go to without fear of infringing upon a territorial cat bed.
Modifications should be made to ensure a safe escape or getaway at all times for the cats- tall, sturdy cat trees and other elevated areas. You want the cat(s) to be able to get away safely if the dog tries to chase or annoy them.
Even if the pets become friends, the play styles between a dog and a cat will always be a little off, so the option of escape must be available at all times.
Lastly, make sure the dog cannot access the cat’s food and water dishes by keeping them up high or blocked off. Do the same for the litter boxes. You will want to stop the dog from eating anything out of the litter box and you will want the cat to have continued privacy (and not cross paths with the dog) when entering and exiting their bathroom.