Before you ever bring a new cat or kitty into your home, make sure your dog knows 2 basic commands: "Stay" and "Leave It." You will be saying those words a lot over the first couple of weeks. So practice with your dog to make sure he knows them before you bring home your new cat.

Stay

Start by saying "sit" while your dog is at your side. Hold the leash in a straight line up from his head with no slack in the leash. Open your palm in front of your dog's nose and say "stay." Step out in front of him so you can block him from going forward. If he moves, snap the leash and repeat the command. If he stays, return to the position next to him. Tell him "Okay" and praise him. Keep practicing this until he stays every time.

Leave It

With your dog in a "Sit-Stay" position and your hand in a fist, with flat surface up, show your dog a biscuit with the other. As he reaches for it, say "Leave It" and pop him (not hard, but enough that he feels it) under the chin. Show the biscuit again, repeating the "Leave It" command. If he hesitates or turns away, then praise him. Doing this twice is usually all it takes for your dog to get it right every time.

You can now bring your new cat home (keeping him in a carrier for now) to your old dog. Put the cat carrier in a safe room, then bring your dog in on a leash. With the cat still in the carrier, let the two look at each other. Let your dog sniff, but if he gets too excited, use the "Leave It" command and praise him for minding you.

Take your dog out of the room, close the door, and then open the carrier door so the cat can come out when he's ready. Allow both animals to get used to each other's scent for a couple of weeks, then put a baby gate across the door to the safe room to keep the dog out. The cat should be able to choose how much interaction he wants with the dog.

Do not ever tolerate aggressive behavior from your dog. Just keep a leash on him until everything is settled down, and use the "Leave It" and "Stay" commands to keep him under control.

Some cats and dogs will always just tolerate each other, while others will become the best of companions. Just be patient as all of these things take time.