How old is this dog? He sounds like a reckless teenager.
Is he neutered?
How big is his vocabulary?
How much do you engage him every day? Or is he in recess to do as he pleases most of the time?
How well does he listen - in the house? Outside? At distances? With distractions?
This is an incredibly smart animal and has a huge work ethic (he should be able to stay on task a long time). This requires that you have a lot of work and responsibility to create success. He is also the kind of dog that could change your life. When you really step up to the plate and he is given a chance to show you how incredible he can be - you could have an amazing relationship.
The picture you present is so much bigger than his energy with other dogs. It's about his place in your life, his education, his self control, and he needs to be in the habit of listening to you and looking to you for advice, which means that you need to spend lots of time with him - teaching, practicing, and adding higher levels of distraction to get higher levels of impulse control and obedience.
Every time he gets into a fight it is failure, so you need to set him up for success by using these opportunities as teaching moments.
He needs to learn about personal bubbles (go to the podcast we did a few months ago). Everyone has a personal bubble and he is oblivious about it. It starts at home - does he respect your space and energy? Can you ask him to go out of a room and he stays out? For how long? Can you have people in a room jumping around and acting crazy and he can maintain self control and NOT jump all over them?
You should teach him how to approach other beings calmly. Establish bubbles around tons of things: toys, bones, his food, at thresholds, people, dogs, cats, etc. Practice approaching dogs that you know are not going to overreact. Have the other dog sit/stay while you heel your dog in a square (not a circle) around the other dog. As he is successful you can change the approach from different angles as you build towards walking right up to another dog and he doesn't react, but stays beside you calmly on a loose leash. From there you can work towards calm greetings. But if he can't be calm 30 feet away from another dog then it isn't going to get any better as you get closer. So you have to begin at distances that he can stay calm in.
Teach him how to play with other dogs just like you teach your children how to play properly, and how to back him off if his energy gets too high. You should be able to say "easy" or "gentle" or "enough" as his signal to calm down NOW! This takes awareness on your part to see the changes in his energy so you can slow him down proactively. You can even start by teaching him how to play with you and give it words like "let's play" and "easy" to mean bring your energy up and take it down.
Can your agility teacher recommend a good obedience class? A good socialization class?
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended