The temperament and characteristics of the Lhasa Apsos that make it a great watchdog (i.e., its assertive, intelligent, & independent nature) can also make it difficult to get along with other dogs.
First, the Lhasa Apsos tend to be dominating, more so than other breeds. Dogs need to know who is boss - if one dog is clearly submissive to a more dominant dog, they'll usually get along; however, it's not immediately which dog is "boss"; they'll immediately challenge each other, and if one doesn't back down, it will quickly escalate into a fight. Compounding the problem, many Lhasas are possessive of their food and toys.
If you are bringing a new Lhasa Apso home and you already have one or more family dogs, follow these steps to make everyone's , and every dog's, life easier:
The established family dog will consider its home THEIR turf, so make time to plan an initial meeting between the dogs in a neutral location, such as a neighbor's fenced in yard or enclosed park that neither dog has visited or explored. Don't go alone. Bring a family member (preferably) so that each of you can handle one of the dogs.
Positive reinforcement works - especially for the Apsos; do not give negative attention when either dog does something you do not like, i.e., scolding or punishing. For most dogs, and - again - especially the Apso, ANY attention is better than no attention. Too many new owners accidentally reward and reinforce the very behavior problem they are trying to eliminate. Focus on allowing your dogs to have calm positive experiences with each other right from the start: let your dogs sniff and greet each other normally. Talk to them with calm verbal affirmations. Let them know you are all part of the pack - and that the two humans are the leaders of the pack. After letting them play for a while, start to gently train both dogs to "sit" or "stay", and when that is successful, let them interact again. To wind down and relax, take them on a walk together, allowing them to explore and play with each other along the way.
As Shakespeare so aptly noted, "The course of true love never did run smooth," so expect some rough patches. Pay close attention to your dogs when they interact. Try to catch any changes in their body posture that starts to show defensiveness: hair standing up, baring their teeth, deep growling, a stiff legged walk or a prolonged stare. If one or both dogs start getting defensive or aggressive, immediately separate them and switch into positive reinforcement training mode, getting them to "sit" or "stay." If that is successful, let your dogs interact again. It is imperative that you are in firm control of dog and that you know how to train a dog.
While it is unlikely at this point that love and friendship will break out between your dogs, some sort of detente should start to take shape, and then it is time to take them home. Most owners suggest letting the new dog enter the house first to reduce a territorial "turf" response from the more established pet.