Just discontinue services with your current farrier. No need to fire him and give him a reason. Call him up, cancel and say you'll call him if you need him.
I would definitely go after the farrier that the new boarder brought in. If he's not "good", he's at least better than the one you have now and was able to spot your horse's poor farrier work.
Is the betadine for thrush? I tend to attack thrush pretty fast and furiously with peroxide. It can't be over used because it can also hurt the horse. But it clears out the bacteria and dries the hoof up within days if used properly.
And those who were seen dancing were thought to be insane by those who could not hear the music