Bark Stop Barking

why does my dog bark at huge dogs and not to little ones and how do i make him stop barking in the first place

he keeps on barking at em, even the nicest ones like retrievers. but come to a chi hua hua, and he ignores em. my dog isnt that big either. medium realy, and its not the first time he gets attacked by a german sheperd becoz of his big fat mouth. Y is this? how can he get used to being around dogs?

just give his leash a little yank,and say shh...each time he does it do the same thing,also lead you dog with head held high,have relaxing thoughs,,he can read your mind.