Lee recommends the Martingale collar, never a choke collar! A correctly-fitted Martingale collar will never choke your dog.
Martingale training collars: www.canineequipment.com
Lee recommends the use of the Halti and the Martingale using two leashes as seen in the photo above. She recommends the Halti over the Gentle Leader because the Halti relaxes when the dog relaxes; the Gentle Leader remains tight at all times.