I will certainly up the training once again, I do think that is the only way around this, yes training seems to be the go-to answer I don't know why I ask any more... I really like the fact that he is a social butterfly, but it seems conflicting with breed standards, (my original concern) then again I am sure he was not bred under standards (puppy mill) so probably was bred out of him at some point.
Breed standard calls for them to be aloof, but is that in general or around people, dogs, all of the above? I think that you have a young dog that wants to have fun. He knows that the dog park is play time, he just doesn't understand that when you say its done its done. He is probably in a very excitable state at that point. I would think that you could try to go to him instead of calling him to you(you are probably pretty close to destroying the come command). You will probably have to calm him down, that is the switch your looking for, he has to learn how to calm down just as fast as he gets excited.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD