We want to switch to automatic debiting of a flat monthly fee from members, but we're not there yet. For now, we need to make sure that we don't let members stick around, using our services, even when they've stopped paying. Quite frequently, members disappear and stop responding to attempts we make to contact them. Our bylaws allow the Board of Directors to vote to boot members whose balances have been negative for three months. Thus, we set the deposit requirement to three months of costs, so that we can boot anyone who has obviously disappeared, before the point where he's paid less than he's been charged.