I have had Saints and Newfies, both well over 175 lbs. Before you harness either breed, define what you are trying to accomplish. If the goal is to allow them on a tie out at a campsite when the adults are not present..I question doing that at all. If adults are present, rather than a harness I would consider a run line with bungee connection. A committed St Bernard will break almost anything you can tie him/her to. I tied up my St Bernard female (225 lbs) to the bumper of old full size Ford station wagon. While talking with someone about 20 feet away, she pulled the car out of park and rolled the darn car over to me.