I obviously wasn't with the OP that day and will not pass judgement, but I disagree with the general disdain towards dog parks in this thread. We live 2 blocks from a big city-owned field that is used mostly as an off leash dog park and I have taken my dogs there thousands of times over the years.
I believe that letting your dog run off leash around other dogs and people when they are young is absolutely priceless in socializing them into a happy, normal, and well-balanced dog. They need to burn up energy, learn how to rough house and yes, defend themselves on occasion. You have to keep a close eye so things don't get out hand but sometimes a challenging situation can be a good learning experience in my book. This is how we grow. And frankly we are talking about German Shepherds here, which are a large and highly intelligent breed that should have no troubles handling themselves in the general public. I'm not claiming to be an expert or telling other people how to raise their dogs, just sharing my philosphy.