Canine Behavior

Question
I have a German Shepherd mix, about 9 years old, that I've had for about a year. He is extremely calm and has never shown any aggression toward people or animals. Little kids can can wrap their arms around him and he never responds in anger or fear. He gets along just fine with my 2 cats. He does not know how to fetch and won't even play tug of war: as soon as you pull on the other end he lets go. The main way he plays is by grabbing one of his stuffed toys in his mouth and shaking it like crazy. I recently acquired a 5 year old Lhaso Apso. When the Shep. mix shakes the toy in this manner, the Lhaso "attacks": he growls and snarls and will charge the bigger dog. I had to split up a fight last night and got bit pretty bad. When he tried it again, I stood between the dogs right away and gave a firm command to the Lhaso to stop, but he tried to run between my legs and go after the Shep. mix. again. In general, they get along OK, but I see this aggression from the Lhaso when the Shep. plays, and also if the Shep. gets to close to me when the Lhaso is next to me (like on the couch, for example). I walk them together, they sleep next to each other and I can leave them alone together all day without incident; but this aggressive behavior from the Lhaso happens at least once a day, sometimes more. What do I need to do to curb this behavior? I would appreciates your feedback. I am not sure if the Lhaso is afraid or asserting dominance. Thank you.

Answer
Hi Pamela -

Congrats on your new pup!  This is a very serious issue and I recommend you consult a trainer in your area ASAP.  Where did you get the lhasa?  Most shelters will want to do a meet and greet with the family (including other dogs) before placing a dog. That way the dogs meet in neutral territory and you can evaluate how they get along.  Unfortunately just like people, not all dogs get along and it has nothing to do with them both being male.  I have two males and I know many people that have two male dogs that are the best friends.  Are both dogs neutered?
I am not sure how long you have had the Lhasa since you said you "recently" acquired him.  It sounds like he is trying to assert his dominance over the Shepherd mix as well as take ownership of you.  He is feeling out his new surroundings and finding his place in the pack.  This breed can be a challenge to train, but try to use a reward based system and keep it positive.  If you google temperament of a Lhasa you will get some insights on this breed.  I have included a link to get you started.  Be kind but firm with the Lhasa and make sure he is not getting spoiled or extra privileges like getting on the couch because he's a small dog.  The tricky thing about this situation is that even though you can and should be the dog's leader, doggie social dynamics have a definite pecking order.  There are no equals in a pack.  If the shepherd is ok with being the less dominant dog this situation should resolve itself in time with proper training and supervision.  Dog fights can be emotionally devastating and financially draining so please try to supervise them until the situation is resolved.
Please consider working with a trainer or contacting the previous owner or shelter before this situation escalates for more insight and advice.  They may know more about the lhasa's history or behavior issues it had prior to you adopting him.  Best if luck with your dogs!

http://www.dogtemperament.com/lhasa-apso-temperament/