The Squire is one of the absolute best tanking jobs in the game. As a Strength based job it gets a high amount of HP and this is only furthered by it using Leather Armor. His damage output with Knot of Rust is directly tied to his HP, and the ability can also be used to interrupt enemy channeling spells, so it works very well as a supplement to his role. If you load a Squire up with defensive gear and have a supporter at the ready, not much can break through your wall.