Thanks to everyone who got back to me about scene 06! I took all the comments on board and have spent the last couple days fixing and finalising the scene. It looks great now, and I've passed it onto Erin for clean-up.
Here's the scene with the new dog and ball layers:
I fixed the slide on the Dog's feet which itself re-timed the run, so now the whole thing happens a lot faster, which a lot of people felt should happen. Because of this I then had to re-time the ball as the Dog began to overtake it. I then re-drew the Dog Walker (who I've affectionately renamed Doug Walker after my dear friend, Doug Walker) to match the new frames, and altogether they look like this:
Finally, I added in the Girl layer to see how everything looks so far, and it looks AWESOME! The new timing of the Dog, etc, couldn't have worked out better! Very chuffed with how it's all looking now: