How do we stop him from barking?
Our GSD is 5 months old and likes to bark. A lot. When he's at the dog park he barks at the other dogs, or if we're sitting outside and he sees another dog he'll bark at it (if we take him to PetSmart too, he goes nuts barking). It's not really an aggressive bark, he just does it when he's excited or wants to play, but it sounds aggressive and people don't like it (especially at the dog park, until they realize he's just a puppy and doesn't really want to eat their dog).
How can we stop this behavior?