When Cairo was coming into his manhood which was around the later part of his 4th month he began to try to dominate every dog (male or female) at the dog part. We were in the smaller dog pen, so there were plenty of smaller dogs for him to dominate. I recognized the behavior (not full mounted, but the arm on the back) and we didnt go back until he was fixed. Major difference.
I would suggest going to a Petsmart and doing your normal commands there. It is so busy and loud there that you can practice getting his attention.
Having an intact dog at the dog park is a big challenge. You dont want to take treats into a dog park in case some one else's dog is food aggressive and you have to feel confident you can pull his attention away from his interest when you want.
I would think any kind of training that included socializing with other dogs would be a big help.