In many cases, dogs and cats can coincide peacefully. In other situations, not so much. The good news? Chances are, you can restore harmony to your household if they are having problems getting along.
The prey drive, in some dogs, can be very strong. Something moves and the dog is after it. But there is an even stronger drive, the drive to please the pack leader. If dogs, in the wild, don't follow the rules, they don't remain part of the pack. Dogs know they need a pack in order to survive, so they follow the rules. Rover doesn't know that he’s not living in the wild. He knows he's part of our pack.
It may, or may not be easy or quick, depending if the dog is just being exuberant or if it is really going for a kill. But the pack leader sets the rules, and if it's a rule that the cats are off limits, dogs can learn to respect the rules.
We recently worked with a couple with two big labs whose cats were living in one room and never came out. Whenever the cats showed themselves both Labradors immediately went for them. Towards the end of our first session, the cats actually came out of the room and walked right through the living room where both dogs were laying down. The owners were amazed. The cats however, had recognized a change in the dynamics of the house. It was a good beginning.
At another session we worked with a woman whose Min-pin was chasing her cats. The cats would high tail into the back room, which was gated, where the dog couldn't get them. Again during the first session things had changed and her cats sensed the difference. They both came out and curled up on the couch next to her. They began to purr and the dog just lay on the floor calmly.
It's not always that quick or easy to institute changes. Some situations really do take a lot of time. You may have to monitor the situation for a while and make sure your cat has an escape path to safety.
Pack dynamics are definitely involved when it comes to cats and dogs. So is communication. Both cats and dogs primarily use their body language to communicate, but they are a different species, so there can be some confusion. Let's just look at one aspect of their body language, the tail.
If your dog's tail is straight up he's likely to be feeling in charge and may even be "on guard". However if your cat's tail is up, he is likely to be feeling happy and maybe even playful. There are two different meanings from the same body language. If your dog's tail is low and wagging, he's likely to be happy whereas your cat's low tail may mean he's hunting or he might be unhappy. This can create confusion as cats and dogs are likely to initially misunderstand each other's body language. Over time they do come to understand each other's messages.