
I introduced a puppy when the exististing dog was only 13months, so still playful and perhaps not so territorial as an older dog, also both dogs were the same breed.
I took the puppy from the car into the garden for a sniff round and a pee, then bought out the older dog on a lead and let the puppy approach. I knew my older dog was very easy going and had been quite happy for other people's dogs to come into the house and garden. Everything went well and it was just a matter of getting the older dog to be more gentle with the puppy. The only signs of a problem was over food when the puppy stuck her head into the older dogs bowl and got told off. Once was enough, she never tried again.