Just be careful with a single dog on a sled- the x-back harnesses put a whole lot of strain on the lower back- I can see it in your video. I'd recommend getting your dog a different harness like the wheel dog harness from man-mat or a harness from non-stop. It can make a big difference for our long-backed shepherds to take pressure off the lower back and hips.
Do you have give/bungy in your tug line to the sled? That can help too.
Your dog has super drive for the work though! Keep it up!
Yes there are special bungee ties that he is tied to on the sled. We NEVER use non bungee'd lines for anything Scootering or the sledding. This was the only time we have tried the sledding. Where I live were lucky if we get snow anywhere deep enough for it. Could you pm me which type of harness you are referring to? If it is something we are going to continuing doing I will look into another one But he loves it. He loves to run!!
I've included harness information below. I figured I'd post here since there seems to be some interest in ski-sled sports with the GSD. I race my malinois and husky- my GSD just never had any interest/drive for the work.
The trouble with Non-stop is getting the product over to North America. If you are really interested in buying something from them- they are based in Norway- let me know via PM and I can provide some more information.