When I worked at The Meadows in Washington, PA - a harness racing track. I was a groom for many years. The pacers would always get rubbed raw spots on their legs front of front legs, and back of the rear legs from the hopples when it was a muddy track.
The old timers used rendered bacon grease (which worked great for regrowing hair and toughening the skin) HOWEVER on a GSP I would not recommend it.. They make a product called "Hopple Chafe" you can order it online from Big D's Harness Supply in Ohio. Shake the bottle up really well before you use it. Rub it on the spot as many times a day as you can and it will grow the hair back. I dont think the dog will lick it as it does not taste very well.
I have used it on dogs before when they have had a rub spot of any kind and it works great.