My home-made processing station is an old metal yard swing frame on which I bolted a board and attatched the cones. Even though it's free-standing, I still don't like to have the blood spattering around, fearing it will attract vermin or predators. So I always hold the head after slitting the sides of the necks so I can keep it from flopping around and direct the blood into the garbage can below. Even then there sometimes is a bit of a splash. If I were doing it on the side of a building I'd want to protect it too, with something easily thrown away or hosed off. You could use a shower curtain liner from a dollar store to go cheap, it could probably be re-used many times before it got too worn. I like the idea of the plastic feed sacks, tack up several as far as you think the blood might go.