How would I get my dominant male dog to accept an adult male cat coming into the house?

Hi, sorry but I would think twice about getting the cat. ANimals are animals. You can not watch them every minute and some one could get hurt (or worse). I had 3 house cats and took in a female German Shepherd puppy 6 months old a few years back. They all got along great, even slept together. Then one day the dog began circling wildly near my kitchen window, and whining.. all excited. Suddenly and so quickly I could not stop her even though I was right there , she ran and grabbed a cat who was sleeping on a kitchen chair, in her mouth and began shaking him violently. When I tried to pull the cat out of her mouth, she would NOT let go. I had to work hard to pry her jaws open, she was determined to kill the cat. Finally I got him loose, he ran limping, hid under the sofa and would u believe the dog STILL was determined to get him even though I was yelling No at her she actually was moving the sofa to try to get to that cat. I ran and got her leash and clamped it to her collar and tied her to a large chair. I shoved the cat in a carrier, locked the other 2 cats in another room and drove to the emergency vet. The cat had a broken collar bone and had to be caged for 6 weeks for it to heal $$$$$$ at the vets, I felt terrible asked the vet what the H--- made the dog do that.. he said apparently from my story the dog spotted anothr animal out the window and went into kill mode and displaced that on the cat. He reminded me they are animals and do not think like we do. I was sure he was right as I had smelled a skunk right around that window the night before and that day. I re-homed the dog with a nice friend who had always loved her and was happy to take her. This friend could not have a cat,she was highly allergic to cats but not to dogs. A purebred Sheperd dog, already spayed, was much easier to place than 3 older cats. So back to your situation, just remember it could be disaster. Be careful and good luck. u sound like an animal lover that would not want to see an animal hurt. Take care.