Start with a big sheet of plywood (at least 4 feet square). Using tape (or paint) and a sharpie, divide it into 100 squares and number them. Then construct a frame covered in chicken wire to surround the plywood – make it at least 36 in. tall, and consider covering the top with chicken wire, too. A couple of days or so before your event, acquire a live chicken. Lay the plywood out on the floor at your venue, and install the chicken-wire frame over it. Keep the chicken in a smaller box/kennel/crate until it is time to play the game.
Once you open the doors at your event, start selling the individual numbered squares as chances in the game. Shortly thereafter, start feeding the chicken lettuce and some grain – and don’t be parsimonious. Let the chicken feast.
When the time is right to play the game (as determined however you wish; although I’d try to get at least half the squares sold first), make an announcement, and gather the crowd to watch. Take the chicken out of it’s box/crate/kennel, and put it inside the chicken-wire frame, on top of the plywood.
The winner is the guest who purchased the number upon which the chicken poops first.
It is NOT cheating for guests to cheer on the chicken, or try to entice it to move one direction or another, as long as they keep all of their body parts outside of the frame. As someone who has attended more than my share of fundraising auctions, I will say that seldom have I had more fun at an event as when I can cheer on the chicken, to… make me a winner.