Encouraging guests to keep their reservations

I'm curious to know if those of you running supperclubs have had troubles with no-shows? I know it's a huge headache for restaurants. And for anyone with flaky friends.

If you're preparing a fixed dinner for just 20 people, with all ingredients and expenses paid for, and no possibility of walk-ins, a no-show really screws you.

Has anyone collected donations or deposits in advance? And if so, how?