Too rough?

I had a Rottie puppy and a friend brought over a boxer pup they played fine until my pup was tired.  Then my pup growled and went at the other pups throat becasue he had enough and was tired.  We separted the two.  After that we had limited playtimes together and they were fine.

I think you are correct in your interpretation of the situation. Doesn't your dog park have a suggest dog weight limit for using the small dog section?

I believe they separate the dogs at 20 pounds (ours is 25), although it doesn't seem people pay much attention. There have been some big dogs in there the couple of times we went in.

We opted to go in the small dog section because he's so close in weight, a puppy and just getting started at the dog park. We weren't sure how he would interact with the big dogs (or they with him).

But with his outgoing nature and confidence, I wonder if he would continue learning appropriate behavior better with older, bigger dogs. I began thinking that yesterday in watching the interaction between him and one of the larger dogs who was chasing a tennis ball. Milo kept picking up the ball, but allowed the bigger dog to take it right out of his mouth without any protest whatsoever.

But with his outgoing nature and confidence, I wonder if he would continue learning appropriate behavior better with older, bigger dogs.

 
... thats exactly what I was going to mention. Your pup is a large breed, he thinks and plays like a large breed dog. Unless he's unusually shy or has fear issues, let him get "beat up" by the big dogs when appropriate.
 
But my question is, isn't there any other controlled environment he can be socialized in? Dog parks are far from a safe socializing environment, unless you know everyone who is in there with you. One of my dogs has on two different occasions been knocked down and "mauled" by a greyhound whose owner was not even paying attention to her dog. The dog's owner was busy doing something else or talking, and her dog was beating my dog with his muzzled face. Nobody was seriously hurt, but I was very agitated, and he did it AGAIN on a separate day because he came to the park after we had already been playing and I couldn't remove my dogs from the situation fast enough. Point is, people are dumb and don't watch their dogs. Not only that, but your common dog owner has no concept of what is acceptable dog behavior and language. I have been told that my dog was "aggressive" towards another dog and shouldn't be allowed to play. In reality? It was a lab who was overly friendly and wanted to play, my dog had no interest in playing and told him so, but the lab persisted in being a total brat (pushing, pawing, following my dog around)... so she growled and snapped at him. Everyone gets mad at ME for my dog speaking the language like it was meant to be spoken.
Maybe this was the case with the boston terrier your pup was playing with. Maybe he had just gotten too out of control, and your puppy was tired of it. But playing with bigger dogs is also an education, as long as it's "controlled" for your pup's safety... do you attend an obedience class or a puppy playgroup? those are also great socialization grounds!
 

Thanks for the reply.

We're taking him to a dog daycare several days a week, both to get him out of the house to stretch his legs while we're gone and to allow him to be around other dogs in a controlled environment.

The staff there has reported he's been a wonderfully good playmate with the other dogs, and I suspect that it has a lot to do with the temperment evaluation they put the animals through at the daycare -- the dogs there are well-adjusted, so he conforms to that standard. Get him off the leash in a less controlled environment and his untrained puppy mind isn't quite sure how to process everything. I think we're going to limit his dog park time until he's had a chance to grow up a bit and the training starts to take more.

Oh, and he'll be attending training soon. We're just trying to work out the schedule.

Sounds like he was trying to assert his dominance over the other dog.

I have no doubt. As we've gotten to know him better, we realize he's a wonderfully balanced dog with a great disposition who's also extremely confident. He's not afraid of anything, but he's not aggressive against anything, either. He does tend to lay it on dogs who show submissive tendencies, and the times that has happened, he tends to pin them down and start growling at them.

The staff at the daycare reported similar behavior, but said it seemed always to come from other dogs who had been egging him on. When they moved him to the big dog side, he was fine.

I'm still unsure how we should react when he's rolling around with and/or pinning another dog while growling and such ... let them go hoping nothing happens or separate them.