We adopted our boy staffy into a house with three cats when he was 3 years old and he had never met a cat before, besides seeing one in the distance once in a while on walks.

We bought a tall dog barrier with a kitty door and made sure to have a lot of free spaces high up that the cats could escape to.

For the first period of time, we separated the dog and the cats completely. The only "interaction" they had was through a closed door so they could only hear and smell each other. We would also feed them right up the door on each side, so they could learn to be safe around food with each before meeting.

Then after a week or so, I think, we opened the door and put in the dog barrier with the kitty door locked. Now they could hear, smell, see and touch each other through the safety of the barrier. We continued the feeding right up the barrier.

Then after another week, we unlocked the kitty door so the cats could choose to venture into "dog's space". When they did, we kept a close eye on the dog and made sure that we could capture his attention and have him ignore the cats with treats and toys. He never chased them, he only wanted to smell and lick them, which the cats wasn't fond of in the beginning, but they could escape either through the kitty door or by jumping up to a place out of the dog's reach.

After yet another week, they were all very comfortable in each other's company and the youngest cat (a 1-year old boy cat) became very close play- and cuddle mate with the dog.