Unfortunately, some dogs are born dog aggressive. Others are not properly socialized and become dog aggressive. Either way, the golden is dog aggressive. This is not something that they can change. However, they can manage it. Solid obedience training, beginning with the basics and working towards doing it with other dogs around is a MUST. The dog must know the ins and outs of sit, down, stay, and heel. As long as they make sure that they don't bring him to a place where there will be loose dogs, or let him loose, then it will be okay. It is not acceptable to have the dog barking and lunging for other dogs either, obedience training will correct that too.

I'm not sure what class they go to, and other PTers might be able to help me out with links as I can't find any, but there are specific training places where they muzzle the dogs in a greyhound type muzzle and just socialize socialize socialize. They work with the dogs to try and turn the behavior around. I would NOT try that without a trained professional there. If interested I would do some research on that.
Good luck!