My parents all pay in advance either bi-weekly or monthly (they choose and most have chosen monthly). They give me post-dated cheques (I have not made this a requirement, but they have all chosen to do so) and so I never have to worry about anyone forgetting. In the future I think I may even make the monthly pay in advance my general rule (with exceptions for those who really can't pay it all at once) because at least if they leave care without enough notice, you have been paid for the month.