jbennett,
Cassius and I live in San Francisco and we would love to get something going either in San Francisco or somewhere near San Mateo. I work in San Mateo and often take Cassius to Montara Beach which is a nice quiet, clean beach. There is a large dog park at Seal Point on 3rd Avenue and a smaller dog park in Foster City that seem to be pretty well kept. Also there are plenty of very large dog parks in San Francisco.
I do have the same problem with Cassius and other dogs. He tends to scare the other dogs or owners because he stalks them upon approaching them, then pounces on them and is Very vocal when playing. He does play with on other boxer near our neighborhood and they can go for an hour straight.
Let me know.