I keep a blog that seems to be updated in spurts and neglected in other spurts, but there is a series of 4 videos on that blog that are helpful with ideas to fool around with.
https://youtu.be/AMigJKW2nE8 How a good stop and back can help your horse carry himself properly
https://youtu.be/A19POG9wap4 More on Balancing the Driving Horse
All I pay my psychiatrist is the cost of feed and hay, and he'll listen
to me any day. ~Author Unknown