Reply to comment

I totally agree with the previous comment. There's no doubt neutering will alleviate some of the aggression especially toward other unaltered males, but seeing as he is already 5 years old, some of his tendencies will still be there.
I had a somewhat aggressive dog too and the only thing that I found helpful was when I took him to doggie daycare and he learned how to play properly from the other dogs. You may have to start off slower at first in a smaller obedience class and then find a local daycare to enroll him in even just once a week for the socialization, and you'll notice many other benefits in your dog as well. Hope that helps!