Let’s take a look at the situation from your cat’s perspective. In his eyes, his kingdom has been invaded by a frightening monster (assuming the gender randomly here). After some unpleasant encounters, he, the reigning king, has been imprisoned while the monster roams freely. It’s good that you recognize his depression, but now it’s time to address the issue and restore his lost confidence.

I recommend visiting Jackson Galaxy’s website for valuable insights about cats. One of the best things you can do is “catify” at least the shared areas where they interact. Install shelves, invest in a large cat tree, and leave high surfaces like a dresser top accessible for him to jump onto. Place a couple of boxes or a spacious cat carrier in corners where both you and the king cat can be sure the dog cannot reach him.

Additionally, it’s important to learn how to safely reintroduce them. If it were me, I would keep my dog on a leash whenever the cat is around until I am certain he poses no harm. This is also an opportunity to teach your dog the “Leave It” command, which is a great starting point for training.

For the time being, I suggest feeding the cat in your room and possibly keeping him there overnight. Alternatively, you could confine the dog in your room overnight and allow the cat to roam freely. However, this should only be a temporary solution, not a long-term arrangement. It’s crucial to note whether your dog actively chases the cat or if there is only hissing and growling between them. The latter, in my opinion, is tolerable. I wouldn’t prevent the cat from giving a swat or two on the dog’s nose, as long as things don’t escalate further.

Regarding the suggestion of using Feliway, personally, I didn’t observe any noticeable difference when I used it. However, it’s an inexpensive option, so it’s worth a try. The key focus should be on training your dog. Good luck, and I commend you for your dedication to improving the situation for your cat.