The odor that causes feet to smell is the fungus / bacteria building up on them. These types of bacteria love dark moist places like sweaty feet inside a shoe.
If your dogs coat is starting to smell like feet, I would first give him a bath. After that make sure he is not in a location where his coat would be wet / damp all the time. As always he may have some sort of skin condition or infection, so CONSULT YOUR VET.
Normal smell of dog body oder is something along the lines of Fritos or Doritos not feet. Also, GSDs should not have baths frequently because it removes the protective oils from their coat / skin and causes skin dryness and irritation.
