Do your dogs and cats get along?
If the answer is no, you are probably frustrated with keeping them separated and making sure no one terrorizes anyone else. When I got my first cat, she absolutely hated one of my dogs, and that same dog tried to eat her every day.
With many sessions of confining them in the same room and correcting the dog every time she would try to go after the cat, I was able to help them get along. But the dog wasn't the only one who needed correcting. Many people who own cats and dogs think that the dog is the only trouble causer. Whoever started the problem needs to be corrected.
I would highly recommend having a professional come in if you are having serious dog and cat issues, because they should know how to handle each. If your dog and cat problems are related to either animal having medical issues and simply being grouchy, the other animal can be taught to give the other space. A lack of spatial awareness and respect is usually the root of dog and cat issues.
Cats and dogs have some similarities in their body language, but many differences. Simply because the dog's instinct tells it to chase or play with small non-dog animals, it generally wants to play or catch the cat. And simply because cats send off a vibe and body language cues to other cats that say "go away", it assumes that the dog will pick up on this vibe.
So the dog needs to be taught to interact with the cat very gently and mostly avoid the cat, and the cat needs to be taught that anger towards the dog is unacceptable. Harmony is absolutely possible! My dog and cat are now best friends. My cat rubs herself against my dog, and my dog licks my cat's face.