We used to take Max to the dog park all the time when he was younger but once he hit puberty, we've stopped. Around 6 1/2 mos.
It's not that I don't trust him. He loves other dogs. We too have always been complimented on what a sweet boy he is and how obedient he is. But I don't trust the other dogs in the park. Namely, the owners of the dogs.
Just because you exercise your dog as well as bring him to the park, does not mean all owners do. Maybe it's just the park we've gone to, but I find the owners let a lot of rude behavior slide and once Max hit puberty, he doesn't like rude dogs. He's never attacked or been the aggressor, but he does stand up for himself.
Most dogs will get the idea, but it's that one that won't that will be a problem. And there's only so much you can do to keep that dog away from your dog. Especially if the other owner doesn't care, or worse,
likes the fact their * insert breed here * is being dominant over the rottweiler. What they don't understand is, the behavior isn't dominant, it's rude.
Just remember, if something does happen, it's always the rottie's fault. No matter what the situation.