I assume that you are talking about the prop walk when you are backing up?
Try this - goose the throttle real good when you first get into reverse and then back off a bit as soon as the boat
moves into reverse and use the rudder
to bring the rear end around, and then give it some more throttle.
Whenever I am backing into a tight place, I like the boat's momentum doing the work
, not the prop. When the rear end is entering the slip, I'm in idle forward and ready to goose the throttle to slow and then stop the boat exactly where I want it.
And with practice, You will have the rear end pointed the opposite way just enough so that when you goose the throttle in reverse, the rear end will point where you want to go.
Backing down on a sailboat is always interesting fun!
The first time I tried it on a decent size sailboat it seemed to have a high pucker factor, as I recall