Happy 4th of July! I'm afraid there aren't a whole lot of patriotic dog movies out there, but you might want to check out Three Wishes (1995) or The Pooch and the Pauper (2000). Born on the Fourth of July (1989) also has a handful of dogs in it including a Catahoula Leopard Dog, but probably not worth rushing out to get just for the few seconds of dog footage.
The trailer for the book Wonder Dogs: 101 German Shepherd Dog Films went live today and you can see it below! Have a happy and safe 4th!