brachy breeds have enough trouble breathing, haltis press on the nasal bones and constrict breathing further or can cause sinus swelling which in Dogues is dangerous. My boy started on a correction chain, ended up on a flat collar he was so obedient. The way you use the chain is attach it to your normal leash and let them have the whole lead. Just before they pull, give it a sharp flick to constrict the collar, then call the dog back to you immediately. The dog will learn pressure = correction but to stick next to you on a loose leash is really rewarding make sure you make a fuss over them whenever they are focussing on you and staying near you. Also never wrap the leash around your wrist, very dangerous with a large dog.