How old is your dog? I'm assuming by your comments that your dog is not trustworthy around other dogs and people?
I'm taking my dog to a behaviourist in Guelph who offers a good program in working with reactive and agressive dogs, and generally dogs with issues. She also offers obedience programs and is an owner of a GSD. Her facility has great puppy classes that allow for the puppies to play off leash.
My dog is not that bad, but we did have an incident which concerned me so I went this way. I'm pleased with the program thus far.
Dogs in the Park - solving behaviour problems in dogs