Introducing two dogs is a delicate operation, and one you shouldn't rush. The key is to make your resident pooch feel unthreatened by this new "intruder," so take your time and allow them to get to know each other in stages before leaving them alone together.
Stage 1 - Keeping Them Separate
Keep the dogs separated for a few days -- don't even let them meet. Instead, keep them in separate rooms and let them take turns roaming the house. You may even swap their blankets and toys after a day or two. All of this introduces them to the idea of sharing the home with another animal, and they learn a little about one another from their scents.
Stage 2 - Walking Them Together
Take your dogs on a walk, either just in the yard or around the neighborhood. Do this by enlisting a partner to walk your new dog while you walk the other. As you're walking, have the other person come up to you two from behind -- this prevents the dogs from becoming too excited at the sight of each other. Give the dogs a few moments to acquaint themselves with each other, which will be easier now that they recognize one another's scent. Just a minute or two is enough, as excessive sniffing can lead to aggression. Once they've met, praise them both before you and your partner walk the two of them home together.
Stage 3 - Monitoring Interaction In A "Shareable" Space
Allow the dogs into the house together, where a shareable environment should be awaiting them. This means that they have enough resources to ensure they won't feel the need to compete for them -- for example, two water bowls, two food bowls and plenty of toys. Monitor their behavior. If the dogs fight over a resource, including your attention, take that resource from them.
It's important that you show your "old" dog the same attention to which he is accustomed. If his patterns of behavior are interrupted by the "new" dog, he'll see that dog as a threat to his lifestyle. Similarly, don't treat the new dog to things the old dog isn't party to. For example, if your old dog isn't allowed table scraps or a certain type of treat, don't give them to the new dog.
Continue monitoring their behavior over the next few days while the dogs get used to each other. They may engage in play fighting to determine who will be the dominant pooch in your house -- for example, they may wrestle, chase and even mount each other. Allow this natural behavior to go on, so long as no one is getting hurt. If the dogs become vicious or violent with each other, consult a professional trainer or behaviorist.
By Tom Ryan
Pet MD: Introducing a New Dog to Your Resident Dog
The Ohio State University College of Veterinary Medicine: Introducing a New Dog to Your Current Dog
Humane Society of the United States: Introducing a Dog to Other Pets
About the Author
Tom Ryan is a freelance writer, editor and English tutor. He graduated from the University of Pittsburgh with a degree in English writing, and has also worked as an arts and entertainment reporter with "The Pitt News" and a public relations and advertising copywriter with the Carnegie Library of Pittsburgh.