We use harnesses on my pups until they understand how to walk with me gently without pulling. My far away harness of preference is called a Balance Buckle Neck Harness. I purchase these from www.clickertraining.com, but I am sure they can be found in other places. This harness has six adjustment points, so it is easy to adjust it for complete comfort for the dog. I love it for times when I am off the ranch with the dogs because they cannot slip this harness! It is also quick to put on the dog; this is important to me here at the ranch as I am always in a hurry.
Pups twelve weeks old to five months old or so fit the Med/Lg size. As adults, they wear the Large size.
I use the front attachment point with pups as they learn to walk calmly with me without pulling. When they are good at that, I switch to a collar here on the ranch, but for the life of the dog, I use a harness off the ranch for safety.
One of my pet peeves, with my dogs or with livestock, is being pushed at as I come through a gate. I begin to teach the pups gate manners by six weeks of age. I also teach the pups to stand calmly while I put on their harness and how I would like them to come through a gate.
To do this, I position the pup in relationship to me and to the gate exactly the same way every time. My pups/dogs are taught not to come through a gate unless they are wearing a harness and leash or collar and leash and are positioned to the gate opening.
This is a lovely system. It makes it very clear to the dogs what my expectations are. With adult dogs, I take this training further; the video below shows the early gate training and how to put on the harness I use.