Every time I mention my desire to get a dog, my boyfriend expresses concern that it will eat his face off. And by "expresses concern," I mean "repeats endlessly with varying degrees of hysteria." While I think he's being a little dramatic, introducing your furry friend to your pet (see what I did there?) is a legitimate concern. The dog could feel that your SO is intruding upon their territory, and things could get very ugly very quickly. Thankfully, The Worst-Case Scenario Pocket Guide: Dogs has some helpful tips to keep your SO from having their face eaten off.
Introduce the canine to your significant other on neutral ground.
Coordinate the first meeting at a public place, such as a nearby park. Avoid introducing the two on the dog's home turf, which risks encouraging a dog to defend his territory around a stranger.
Instruct your significant other to approach the dog calmly.
This is particualrly important if your pet is overful fearful or very dominant. Advise your companion to avoid prolonged eye contact (which can be construed as a threat) or immediately and enthusiastically petting the canine (which the dog might find unnerving). Coach your partner to greet the animal in a low-key manner. Later, if the dog seems amenable, your significant other can pat it on the back. Do not overdo it.
Praise your dog for good behavior and offer him a treat. Even better, have your significant other offer him a treat.
Wear a garment that has been in contact with your new companion.
When alone with your dog, wear an article of your partner's clothing. This will help familiarize the canine with your significant other's scent, making your dog more at easer when he actually encounters your significant other.
Have your significant other feed the dog.
Occasionally a canine may develop dominance issues with a newcomer. To diffuse this, have your new friend feed the dog for a while. Being in charge of the animal's sustenance will make the person seem "dominant" in the eyes of your pet.
A "significant other" might be a lover, a new roommate, or a newborn baby. Most of these steps also apply to introducing another dog, cat, or llama.
If your dog's suspicion or distrust of a new acquaintance seems unshakable, do not dismiss it. Canines are experts at "reading" human personalities and intentions. He may understand your new friend's true nature far better than you do.