Martingales are excellent walking and training tool enabling a gentle correction but are not suggested as an all day collar left on without supervision.
Measure widest part of head and high around neck as diagram above shows. Martingales should be adjusted to fit your dog at the narrowest part of the neck right behind the ears and under jawline when both slides are close to touching each other. Adjust so it will not slip over the dog's head when the secondary loop is tightened as in use, but will when the collar is slack so you can still take it on and off. This setting allows the martingale to work correctly.
Keep the dog next to you with collar under their jawline and on a shorter leash. More of a vertical direction versus in front of you and horizontal. When the dog is next to you and starts to pull, you have control to correct behavior.
I make martingale collars to order so please allow 2 days. Any collar choice can be made as a martingale, just add the martingale upgrade to your purchase.