You can find this exercise on page 67 of the book Synergistic Golf.
Exercise Type: DYNAMIC STRETCH
Exercise Category: BALANCE, FLEXIBILITY, LEGS - FEET
Stand with feet wider than hip distance apart. Place hands on hips with shoulders back. Bend right leg at knee kicking the heel back to the gluteal. Can you touch your buttock? Swith r and l legs 10x while balancing on the opposite leg briefly.