Maybe try a lead until he gets over it?

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Proud owner of Rocky the Yorkie, born July 2008, who came to live with us at 8 weeks old
and
Ellie the Yorkie, born February 2012, who came to live with us at almost 8 weeks

I find that I have to walk my male sheltie by himself he doesn't like any other dog coming after the girls or me so he gets very upset if a dog is growling at the fence or is loose and comes after us. If he's alone with me he will not bother the other dog if I say leave it. So now I usually 4 out of 5 times walk all the dogs separately until the younger girls are finished training. The dogs really like the one on one time together also so it's a win win situation...Jill

I think your dog is jsut being a little bit over protective I would suggest correcting him by saying no any time you don't want the dog to bark. If he continues try squirting him with a water bottle or "time outs" but i think the water bottle will work ebcasue it will distract him.