A German shepherd search dog and its handler, Ronda Luce '74, were credited with saving the life of a 65-year-old Alzheimer's patient recently when they discovered the woman lying in a shallow creek four hours after she was reported missing from a care facility in Poulsbo, Wash.      Luce and her dog, Dyna, found the patient within minutes of the start of a coordinated search. The patient later fully recovered at a local hospital and has returned to her retirement home.      Luce, a physician, lives in Wildcat Lake, Wash.