my friends horse, who I ride, had an abscess last summer, after treading on a sharp stone that when up inside the hoof - the vet couldnt kept in deep enough and the farrier came out and dug up right inside the hoof, and the blood that came out was everywhere, it looked like an abbatoir.
We had to change the poultice daily, and rather than cover the poultice in plastic, the farrier put on a special shoe and made a very strong plastic cover which was held in place with bolts which went right into the shoe. It was a bit strange for him, as you can imagine that it was like wearing platform heels! Fortunately the horse is well mannered, and would let you do anything to him, but I was unable to ride him for many many months.