SARATOGA SPRINGS, NY - Every morning when Tiz the Law (Constitution) goes out to the track for his exercise, there is a Smullen from Oxford, PA on his back. Most days the likely favorite for the GI Kentucky Derby is carrying Robin Smullen, trainer Barclay Tagg's longtime assistant and life partner. Once a week, when the colt has his timed workout, though, Heather Smullen, Robin's 38-year-old niece, has the assignment. It is a challenge, she acknowledges, to keep the four-time Grade I winner to the task while not getting in...