As you may remember, George and I acquired a puppy last May. Stewart was a two-month old, 16-pound bundle of fur. He's now nine months old and clocks in at about ninety pounds.

Just so you know, he has been through basic obedience classes and is now in a puppy agility class with George. He enjoys his classes, did well in them and is as obedient as one could reasonably expect a pup of this age to be. He seems to want to please us. He gets tons of love, is an indoor dog, is fed a premium food on a regular basis, and sees the veterinarian whenever he needs to. He's had all his shots and he does not have worms. He is half Newfoundland, a quarter St. Bernard, and a quarter Labrador.

We are having a serious behavioral issue with him. I like to take him to the dog park once and sometimes twice a day. He has started menacing other dogs over three things: sticks he finds, select dog friends, and us. By 'menace' I mean he snarls, snaps, and does that nasty attack thing where the fur flies and there's a lot of drama. It's very scary.

At first it was mild and only I noticed that he was getting agitated. It seemed to happen after we'd been there an hour so I started taking him home at 45 minutes. But it has gotten progressively worse and to make a long story short, we'd been at the park one minute yesterday when he picked up a stick, took it over to another dog, dropped it and began the scary snarling routine. It was as if he were egging this other dog on to fight with him. When I felt I could safely put a lead on him, I snapped it on and dragged him out of the park, snarling and menacing. I was intimidated by my own puppy!!

I took him to the vet and she finds nothing amiss medically and has recommended a behaviorist who has not yet returned my desperate call. I've never had an aggressive dog before and am baffled by why this is happening. We love Stew but he is going to be huge when full-grown and he MUST be a good, stable, reliable canine citizen for our safety and that of our neighbors and their dogs.

He also does not like other dogs to interact with us or with his small circle of special friends. He will do the same thing if his people or friends are encroached on.

Needless to say, I will not take him back to the park until this is resolved. It's such a shame, as I have access to his littermate, Molly, who lives just a mile from us. Her owners work and were pleased when I offered to pop her into the back of the station wagon when I take Stew and the two of them seem to adore each other and he does not have issues with her. But as soon as another dog arrives at the park, PsychoPup emerges and no one is safe.

Does anyone have experience with something like this? Could it be something he will outgrow? We are terribly concerned because this does not seem normal at all.

Thanks for any advice you can give me.

MarnaLou