Hi, I am not sure what a GSD is (I am allergic to acronyms), but I sure know of a really good trainer south of you. If you want to drive a bit it is in Flamborough township on Brock Rd. just north of 5th Concession Rd. You will find McCann's Dog Trainers on 929 Brock Rd. They aren't cheap but they are very good. I took my late lamented Golden Retriever there for two semesters when she was a bit less than a year old and she learned to become a model citizen. Like most professional trainers, they try to train the humans to work with their dogs and it is a skill that stays with you whatever dog you acquire through your lifetime.
You can check them out here:
http://www.mccanndogs.com/main.htm