Exfoliate is when you dig out all the white chalky-looking sole and get down to the waxy-looking live sole. That's when you know when to stop cutting.
I think the farrier digging out Tuffy's sole is what has exacerbated the problem to the point of him being unable to walk. According to his x-rays, he has no natural cushion in the sole of his foot so when the farrier starts digging, he's taking away whatever small amount of exterior cushion Tuffy had. I've had other horses you could dig out half their feet and it wouldn't effect them but it doesn't work for Tuffy.
On a light note. I took a few pictures of Rocky and my rooster. I think they're friends. The rooster during the day is always in Rock's stall hanging out with him. Today they shared a meal:)