This is one of the more interesting fundraising ideas and should guarantee people keep talking about it for a long time afterwards.
To be able to host a cow pie bingo, you need a farmer willing to loan you one of his cows and a suitable area to hold it (this needs to be an area where no one minds the cow walking around or doing its business — check with the farmer if you're unsure).
Create a grid on the floor with paint or chalk and mark each square with a letter or number. You then sell bets on which part of the grid the cow will deposit a “pie” in. It's a good idea to have some ground rules in place should the “pie” be left on a line or across multiple squares.
Set up a concession stand offering chips, hot dogs, popcorn, coffee, sofa and other snacks to boost profits. Putting on some form of entertainment while the squares are being sold is a good idea too. Once all the spaces have been claimed, turn the cow loose on the grid and wait — the winner picks up a cash prize or something donated by a local business.