Okay, I sympathize on the fact that your horse got a screw in his hoof, that really is unfortunate. However, keep in mind that you were the one who decided to place your horse in someone else's care. I know that not everyone is able to keep their horses on their own property, which is where boarding becomes very handy. When you do board a horse it is your responsibility to tour the facility, get to know the owners/managers and make sure that you feel comfortable keeping your horse with them. If this place is really that unfit for horses, and the management really is that bad, wouldn't you have picked up on that in the beginning after meeting the management and touring the facility?
When I first toured the stable I am at currently, it was great. Clean, the owner was walking around giving out carrots every morning, the horses looked healthy. I started out at the stable leasing a horse there, and I wasn't there enough to see all the goings on. When I bought my horse and boarded there, I was there every day and then you notice more. You should be able to trust the people you put in the care of your horses. Yes, it was my decision to put my horse there, but I don't have xray vision or esp...I didnt know they owners would allow the place to go so downhill. There were nights when I would watch the feeders skip horses and would have to go feed them myself or they would just be hungry that night, out of worker laziness.
But on a positive note, set up our new stalls at the new stable today :) We are trying out rice hull bedding. It is totally self care at the new place, but it is basically in my back yard (1 miles away) so I think it will be great.