Poodle aggression towards other dogs

Question
We have 2 male standard poodles.  One of them, Jake, who is now almost 2 1/2 years old has begun showing aggression towards others dogs.  This started at about the age of 2 years.  Prior to this he LOVED other dogs. We made it a point to socialize him, by regularly taking him to the dog park and always having him enrolled in obedience and agility classes.  I first noticed the aggression in an agility class and it was only toward the new dog in the class that Jake did not know, the other, familiar dogs were all his friends.  The next session of agilty class there were more new dogs and the behavior continued.  We then enrolled him in an obedience class with all new dogs he didn't know and he exhibited the same behavior, although occasionally he would be friendly and want to play.  The trainer thinks he is being possesive of me and has us trying to always have his focus on me and not the other dogs.  He is very obedient, at home, when doing agility and in obedience class.  He is the alpha dog with our other dog, Ozzie, who is 1 yr 8 mths.
Do you have any ideas?  I know that deep down Jake  really would love these other dogs and would love to play with them. It is very upsetting to see him behave this way, he is really a wonderful dog.

Answer
I guess my best guess is the same as you've heard - he is protective/possessive of you.  If he has not been neutered, that may also be part of the problem. A dog has the same sort of testosterone flowing that makes the 2-legged "critters" aggressive at times...

Other than that, I truly have no suggestions....other than continued positive reinforcement when he acts as he should.

I do wish you luck! (I probably would have clicked the "sorry I can't help with that" except that I think it's kind of rude, and it may be that neutering could help).

Another thing (this will sound strange I suspect) is something one of my dogs took when he had some problems (not aggression, but behavioral).  My vet suggested a small amount of prozac each day.  I was taking it at the time, so I'd just take a pill and break it open and put a few grains in some cheese, which he took as a treat. I only used a few grains as he is a teacup poodle.  After a week or so he seemed to mellow out. I kept him on it for several months, then tapered off. He hasn't had the problem since then.  

Good luck!

Kathy