You're right on track. The only difference between what you plan on doing is that I don't have a specific mark for my foot placement. I like that idea, though. What I do is set the cord like you talked about and then step backwards while looking down to get my foot spacing and toe flair out set where they should be. While that is happening I have some sort of GPS thing going on in my peripheral vision (which by the way expands outward significantly when looking downward) that gets my feet and hence my butt positioned right in relation to the cord. Your proposed method is probably better. I had the good luck of getting a spot on depth from a guy in his 50's at Gold's who had competed, so his feedback was invaluable. Then once you get your feet set, set your pelvis, and remember to keep your neck neutral and look down to near where the wall meets the floor.