Shoulder In, Finally!

Today I finally "got it" for shoulder in, with the following exercise:
Begin on a large circle in normal trot. Do shoulder out around the circle with the horse flexed to the outside. Rhythmically step down into the "inside" (of the bend) stirrup, with your leg at or in front of the girth, to "hook" your leg into and around the horse. Then go on a short straight line from the circle, where you will be in shoulder in to the outside of the circle. Then continue around the circle in shoulder out, interspersed with period of straight line of shoulder in to the "outside." Voila, we finally got a "very good" shoulder in! Thank goodness for great trainers who give us just the exercises we need to learn!