Unsocialized Dog

[AChen]

Hi,

So I am have some problem with my 3.5 year old Maltese/ Shih Tzu. So I have had him since he was 2 months old and everything has been going pretty well. However, this was my first dog and regrettably, I did not socialize him properly when he was young. So now he has problems with other dogs. If they get too close to him, he will growl and stare at the other dog. However, he doesn't really go looking for trouble. It seems as if he is mistrustful of other dogs.

Recently, I took in a 3 year old Yorkie/Pomeranian in from a friend. This has caused some problem for my Maltese. He growls and stares down the Yorkie constantly. When the Yorkie makes sudden movements, the Maltese will even lunge and nip. Thankfully he never bites. The Yorkie is always extremely calm and never reacts to any of the Maltese's behaviors. I have, however, been able to get them to sit quietly within about 3 feet of each other.

I was wondering if there were any exercises or activities I can do with the two of them so they bond and build a relationship? Or is it just something that will have to take time and occur naturally?