Question about behavior and need to vent!

[Nothing To Do With Doodles]

I take my dogs to a big field at a horse park so they can run around. There is a very nice bark park there with a pond and ducks and it's far from the road so it's safe. Sherlock, my maltipoo, is not a fan of big dogs, so he usually just stays by my side. He gets growly and snappy at big dogs if they try to pounce on him, if they stand over him and sniff him too long, or basically whenever he feels threatened. Today he got a bit growly at a boxer mix that was sniffing him too long, and out of nowhere, a pitbull* comes flying at Sherlock and tries to attack Sherlock. The dog ripped Sherlock's coat apart (it was fastened together with velcro) and luckily I was right there so I was able to grab the pit's collar. Of course the owners were yards away and it took what seemed like forever for one of them to come get their dog. The whole time the dog was viciously barking at Sherlock and trying to bite him. One bite and Sherlock could have been seriously injured or killed. It didn't help that Sherlock was trying to defend himself and snap back at the dog. We left the dog group immediately and walked around the perimeter of the bark park. The whole time I could hear and see the pitbull causing problems with the other dogs. Finally the owners took the dog home.
The strange thing was that after the incident, Sherlock was trying to mark EVERYTHING in sight. Normally he marks a few things, but he literally went up to every bench, tree, bush, rock and marked it. I have no idea why he was doing this.
Sherlock already had a strong aversion towards bully breeds, and now this is going to make things even worse.
Also, anyone with a little dog that doesn't necessarily like bigger dogs, how did you socialize your little dog to be calm around big dogs? I've thought about putting Sherlock in day care with bigger dogs, but I'm not sure if he would like that....
* in general I like pitbulls and think they are friendly dogs. A bit too exuberant for me though. But WHY would you bring your unsocialized dog-aggressive dog to a dog park!!!!?

[Terri H and Kramer]

maybe I should keep him on a leash for the first 30 minutes or so after we arrive at the park?? That seems to be the amount of time for him to understand that other dogs either don't like that behavior or he settles down and does normal greetings to other dogs...don't get me wrong..he is not so obnoxious that I feel like we have to leave...he just has to figure it out EVERY time we go there!

[Karen, Jasper and Jackdoodle]

It's not ideal to keep a dog on a leash when other dogs are off-leash; dogs react differently to other dogs when they're leashed. The most common thing you find is a dog who goes berserk when he meets a strange dog while on-leash, but when he's offleash, he ignores other dogs. (Jackdoodle...this means you) But if Kramer's okay with it, that might work.
Would it be possible for you to spend the first thirty minutes at the park walking with Kramer away from the other dogs, playing ball, or doing some other activity that will tire him out a little and let him get over that initial excitement? The parks we go to are part of the Forest Preserve, and have walking trails and other areas besides just the big main area where dogs and owners congregate. That might help.

[Terri H and Kramer]

I really try not to keep him on the leash in the park, I have been told it's not good to do that. Usually I take Kramer for a walk before we go to the park to burn some of that excited energy. He just is a big, clumsy excited puppy and LOVES to play with other dogs! When it's obvious he is annoying another dog or owner I do take him to a different area of the park. Sometimes it get really crowded and there just isn't a "getaway" area. Does anyone else have concerns about their dog hurting a smaller fragile dog unintentionally? I cringe when Italian Greyhounds for other fragile breeds are in the park, what if Kramer hurts them accidently while playing? He is almost 60 lbs, after all! Will they sue me? I am beginning to think it's too much trouble to go to the dogpark, even though he adores it. Ughhh! It's like being a new parent all over again!!!