My Rotties love the dog park. Spent most of our walking time at dog parks. It's where we meet lots of other Rotties. No bias there... maybe a little. Hank gets a big bang out of breaking up other dog fights. Bang, right into the middle of it. All the dogs separate and go off and so does Hank. Dixie, at 6 months, is a little tentative with all the other dogs, but her excitement is tremendous. We also walk my daughters 8 lb long-haired chihuahua. Hank is the natural escort for both the smaller dogs. Dog parks are the only place to see 10 other rottweilers in 30 minutes.He's submissive because he is still very much a pup. Would you expect a 12 year old boy to know how to defend them self? I suggest that you stay away from the dog park. Rottweilers are not dog park material. Dog parks are dangerous places...expecting strange dogs to get along is not normal behavior. As I said before, you dog may not be the one starting a fight, but will want to finish one, and be the breed blamed if there is a fight. Vets love dog parks, it's a great money maker for them.
Better to get enrolled in some sort of obedience classes...he will be socialized, and will learn how to train with all sorts of distractions around him. I would also see if you can find a friendly dog that he does do well with and arrange play dates. I've often found that Labradors do well playing with Rottweilers.