That "huge win" feeling is so real. My friend had a mare that would rear up every time the farrier came near. She spent ages just getting her used to having her feet touched at all, little by little. The first time that mare stood quietly for a full shoeing, my friend actually cried from relief. It makes all the slow, frustrating days worth it, doesn't it? What do you think finally clicked for your guy?
Seriously, that mare reared up every single time? I can't imagine how scary that must have been for everyone involved. Horses are so powerful, and rearing is one of the most dangerous things they can do. It must have taken incredible patience to work through that.