Summarize this article in one sentence.
Your dog thinks of your home as her territory, and may feel threatened and defensive if a new animal is suddenly brought in. It can be helpful to begin outside, with the cat in a pen and your dog on a leash.  Start at a distance and gradually approach the pen with your dog. When you get close enough that she notices the cat, stop. Let your dog look at the cat for a few seconds, then say your dog’s name. When she looks at you, click and treat. Repeat this process—let her look at the cat, say her name, and reward her when she looks at you. The idea is for her to associate remaining calm at the sight of the cat with being rewarded. If your dog is too distracted by the sight of the cat to focus, move away from the cat until your dog will reliably look at you every time you say her name. Gradually move closer to the pen, continuing this process as you go. Make sure you give your dog plenty of treats; it’s important that you make good behavior more rewarding than bad behavior. Keep practicing until your dog can do this while standing right next to the cat’s pen. Be patient. The amount of time you will need to spend on this will vary depending on your dog. This is a good option if you are unable to have them meet in a neutral area, or if your cat is distressed by being in a pen outside.  Get the cat set up in a designated room of the house that the dog does not have access to. Put his bed, water and food bowls, scratching post, liter box, and toys in this room. The idea is to create a space that feels safe to him. Give him at least a couple days to acclimate before you begin introducing the dog. Put your dog on a leash and fill your pockets with her favorite treats, as well as a couple treats for your cat. The door to the cat’s room should be open, but blocked by a baby gate. For the first couple days, just practice walking past the door with your dog. Click and treat for a calm demeanor, and throw your cat a treat as well to help it associate the dog’s presence with good things happening. Practice basic obedience with your dog in proximity to the cat. You want your dog to become used to keeping her focus on you even in the cat’s presence, and your cat to see your dog as non-threatening. If your dog is too distracted to focus on you, move further away from the cat until you have her attention. Move gradually closer as she gets used to this activity. Only use this option if your dog is crate-trained—if she does not have positive associations with being crated, she will probably become too worked up to learn effectively.  Have your dog go into her crate and shut the door. Bring the cat into the room. Your dog may start whining, yipping, pawing at the door, or even growling. Let her react in whatever way is natural to her. Again, let the cat set the pace of this interaction. If he does not want to approach the crate, do not force him. Click and treat for moments of silence or calmness from your dog. Let them do what they want for 10 or 15 minutes, and then separate them. Continue these training sessions until your dog remains calm in the cat’s presence. At this point, proceed following the steps described above.
Start in a neutral outdoor area. Make the introduction in your home, using a baby gate to keep the two in separate rooms. Use a crate to keep the two separate during their introduction.