Natural Family Planning (NFP)

Natural Family Planning (NFP): "The TwoDay Method is a new simple approach to NFP. It relies on a simple algorithm to help women identify when they are fertile, based upon the presence or absence of cervical secretions.
If the woman notices any secretions on the current or previous day, then she is probably fertile and should not have unprotected intercourse to avoid pregnancy.
If she notices no secretions on either day, then she is not fertile. "

If it's this easy to avoid pregnancy...