I have a German shepherd/Doberman mix, I've always wanted a purebred GSD, one of the reasons I wanted one was to be able to take it to the dog park. My girlfriend convinced me to adopt my mixed dog, unfortunately my only problem is he seems to be a very dominant oriented dog when it comes to other dogs at the park. You would never imagine him being agressive at all if you met him, but generally he gets into fights with huskies, pitbulls, and other GSDs when I did take him into the park.
He is very obedient, smart, and very loving to some dogs and animals but especially humans; I know for certain it's about dominance because he usually is not agressive to the others when he goes in, before he used to be very anxious of other dogs in general but I have since then mostly calmed him down, however when a new dog came in he always rushed to the entrance right up to the dog, to size it up basically, and depending on the dog, he also "stood over" or at least tried to, which sometimes wound up in him fighting. I would very much love to be able to have him play once again but without the risk of him getting in trouble.