clara4457 gave you very good advice.

I have a dog that has fear dog aggression too.
He can be quite the bully when it comes to strange dogs
and very embarrassing.

The gentle leader works on him.
I use that in more public places.
Using treats and positive training has helped
some too.

When I would pass a dog from across the street,
I would try and stick a treat near him to get
his attention away from the dog.
If he behaved he got the treat.
(he can spot a strange dog that is 2 blocks
away and he will start to get upset.)

A trainer who has experience with aggressive dogs and
uses positive training methods can be very helpful.