We've tried the martingale collar with limited success. After much thought and angst we have decided to withdraw from the Canine Good Citizen class and take it again when Tully is older and neutered. We're not quitters but sometimes reality and common sense take over. There's not much point in setting all of us up for failure and causing unnecessary stress. When I called the facility to advise them we would not be returning I got the chance to speak to one of the trainers and she agreed it was a wise choice at this time. It kills me to waste the investment (the class wasn't cheap) but discretion is the better part of valor.