Notweiler question in re sudden onset of apparent dog aggression

[TwitEm]

Hi--I have a 3 yr. old neutered male Golden named The Great Gatsby. He lost his Rottie buddy to congenital kidney disease and kidney failure about ten months ago. I am waiting for another female Rottie, bitch to be bred in March. So...my question will be similar to one already posted about acquiring a puppy when another dog has issues.

Gatsby was attacked by an off-leash dog about six months ago. Since then, he has been either anxious around other dogs, or lunging at them. Until that time he had never shown any sign of aggression whatsoever. He has been through Puppy Kindergarten, Basic Obedience and is now in Novice Obedience class. Until he was a year and a half went to doggie day care a couple of times a week. The aggressive behavior has generalized to one or two of the dogs in his training class. Only certain dogs will provoke a response. Sometimes he's OK around other dogs, but I am careful about letting him approach even when he seems likely to make a friendly overture.

Since he is trained, he will sit/stay or down/stay when a dog on leash passes. When we are out walking, I treat him every time he passes another dog without incident.

My question is: is this behavior likely to continue? How can I counter-condition him? Is he likely to forget the time he was attacked? Is he likely to get aggressive with a female puppy, too. The dogs he has reacted to in class have been unneutered males, and he isn't likely to react at all when the class contains only a few other dogs.

Some counter-conditioning suggestions would be greatly appreciated. Thanks so much. ***************