First introductions should be outside, preferably in neutral turf. Take the dogs on a side by side walk. This helps tire an active puppy and while providing a happy back drop before entering the yard and home.
It is important that all early interactions be supervised. Whether a new puppy or an older
dog it can take a few weeks for everyone to get used to the new family member and new normal. Watching body language closely during this adjustment period can help prevent future problems. Separate the dogs if you are not able to closely supervise, especially during the first 3 weeks, until they have time to adjust to each other.
Baby Gates, crates and Xpens make great separators so that the dogs can have down time where they feel safe and comfortable. Separate eating areas since new puppies can be overly curious and older dogs may not appreciate a puppy interrupting them.
Make sure there is always an escape route so that the dogs don’t feel cornered. Have a clear path to get away can make the difference in whether a dog goes for the bite or not.
No matter what happens do not punish either dog. Punishment can make a bad association between the dogs resulting in escalation of aggressive type behaviors.
Reward when the dogs are getting along, whether playing with or simply being in the same room, be sure to reward with attention, special treats or even going outside. This will help cement that good things happen when the other dog is around.
Watch for body language that indicates a problem may develop and intervene early with time apart to de-escalate. Older dogs may be tolerant up to a point so watching their eyes, ears, tail position and watch the puppy for signs that he is getting too ‘in the face’ of the older dog and needs time apart to calm down.
Give the dogs time to become acquainted and adjusted. This creates a foundation rather than forcing them into a relationship that isn’t comfortable. Following the Rule of 3s, after about 3 weeks you should see things moving toward a comfortable co-existence and, depending upon the ages, playing together.
Watch the body language. Lots of licking can be a sign of increasing anxiety which means the dog is not adjusting to the new dog. If the puppy yelps and the older dog does not back off but instead escalates it’s time for a break. You’ve hit the 3 week mark with no improvement. Any of these should net a consult with a fear-free professional.