http://www.flyingdogpress.com/sayhi.htmlhttp://www.flyingdogpress.com/aggressionbasics.htmlhttp://www.flyingdogpress.com/aggreasons.htmlhttp://www.flyingdogpress.com/selfpg.htmlThese are really excellent articles by Suzanne Clothier on this subject, see if any of the above fit your situation.
I hate the dog park, we only go in the middle of the day or other off-peak hours when hardly anyone will be there. MY dogs are under control, but too many other people's dogs aren't and I don't think it's fair for the boys to have to keep being subjected to rudeness. I get in arguments with Lab owners all the time, they think because their dog is "friendly" (read obnoxious and untrained) that anything they do is ok. Phyfe doesn't like to be pestered, he won't bite, but he'll roar like a lion and send the other dog running. Then he gets accused of being "aggressive". If the other dog owner ignores it, his boundaries are established, and usually there's no more problem.
A while back someone mentioned their trainer said that what goes on at the dog park isn't really "play" anyway, it's all posturing and jockeying for position. I agree, I run playgroups at my job, and it's the same thing, all the running and growling is just low-level pack positioning, it has nothing to do with play as we would conceive it, no matter how good natured it is.
The other day we went and some other big paws were there, a Newfie, two Mastiffs, and a St. Mix. Everyone was happily having a good time, exploring and sniffing, playing a little tag, but no frantic activity-they're all 3 years old or more, it's just not their nature. Then a lady with a Yellow Lab showed up. The Lab kept charging the big guys, jumping at them, play bowing and barking (it was actually kind of funny at first, everytime he let out that shrill play bark Phyfe and the Mastiffs squeezed their eyes and flinched a little). None of the big dogs were comfortable with that game, but the Lab refused to back off. He even ran completely UNDER another dog a few times. Earnest was the only one that understood it, but he's half Lab, so he half-heartedly played back, but you could tell he really preferred his other buddies. We moved to another side of the park, the Lab came, too and the owner called it once or twice, but it didn't listen. Finally the big dogs were getting irritated, I was afraid if Phyfe did his "back off" noise that the other dogs might jump in and fight, so I leashed him and walked over to the lady, I told her that her dog just didn't fit, and could she keep him on the other side of the (huge) park. She got nasty, and said "not my fault your dogs are aggressive, BEASTS like that shouldn't even be allowed to breed, let alone come out in public!" Not the first time I heard that one.
So six to one, and she got what she wanted, we all leashed up and left, you know what would have happened, if her dog got so much as a scratch the big dogs would have been at fault, just 'cause they're big. This particular park exists mostly because of the efforts of the people involved in Newf/Great Dane rescue, it's a shame that we can rarely enjoy it.