My thoughts? I think you need to be trained, not him. And, I don't mean that in a mean way.
Just because you live in a big city does not mean you can't avoid certain triggers. Many times dogs will carry on when on a leash because they are an extension of the person holding the leash. Here is a link that might help:
https://positively.com/dog-behavior/...sh-aggression/
Google Victoria Stilwell and Tamar Geller .. they are both awesome and have lots of positive dog training tips!