My dog has become possively over toy objects at the dog park. How do I fix this problem?

Dear Ed Frawley,

I have been to your website many times the past few months since I purchased a GSD puppy in January. He is 10 months old, a great house dog and is sweet to my Pomeranian and my two cats (never had problems before with them getting into actual fights, only play fights). I have been training him with a prong collar and using long leashes to teach him sit, heel, come. I am moving slow with his training but I am still trying to find a reputable obedience class in my area. He responds nicely but I still have work to do. Ever since the beginning of our relationship I have taken every precaution to keep him below me in the "pack rank" so that I am seen as the alpha. He is extremely smart and has a good amount of prey drive.

The two problems I have had to deal with since he turned 5 months old are his possessiveness with objects like tennis/soccer balls at the dog park, and choosing a young dog to become dominant aggressive with almost every time I have been to the park. His aggression with possessiveness has never been addressed to me or my fiance with whom I live with. I am afraid that if I do not Correct this problem he may become aggressive to the point of not being able to socialize even with the older dogs because there are young dogs at the park.

He is great with older dogs and dogs who are equally dominant back to him, but he becomes very dominant aggressive with the younger dogs and puppies even if they submit. He has not drawn blood yet but his nipping, holding and nasty growling has gotten out of hand. I want to be a responsible dog owner and fix this problem but I have am not sure how to do this correctly. I also don't want to deal with an attack that leads to a lawsuit, an upset owner, or an injured dog.

If you could respond back I would truly appreciate it. Koda (my GSD) is a wonderful dog and I want to be able to share that with other people.

Thank you,
Gina