Interesting thread. Bijou is very friendly but submissive when off-leash - she'll engage play with every dog she sees but lets them know almost immediately - through her play - that she can be dominated. She's also much more likely to simply plod along and sniff and investigate independently when she's off-leash at the dog park. When on-leash (at least for walks in the neighborhood, I haven't taken her to the dog park on-leash) she's enormously intense about getting to other dogs, people, squirrels, fluff, whatever's moving! She strains at her leash and leaps up on her hind feet. Now, she's just one year of age so she'll settle down, I'm sure, but if she were to meet dogs at the dog park like she interacts with dogs when she's on-leash, there would be barking and challenges and all kinds of "different" behaviors than when they can simply roam, sniff, trot along for a few yards together and then do something else. I sometimes feel anxious when I'm at the dog park, to be honest, because I don't know any of the other dogs or their owners and I have to hope that their dogs are friendly and curious like mine, but I try to go anyway, and give Bijou some "normal" doggie exposure. She doesn't ever appear scared or angry, so I try to follow her cues and stay very close to her when we're there. I always wear her leash around my neck so if I should need to leash her immediately I can. It's a tough call.

You might consider making a little badge to wear (you know those dorky, "Hello, my name is..." type badges?) - yours could say, "Pup in training" so that folks understand your decision to keep your dog on leash.