Natural contraception is embraced in this week's "Mind&Body" of The West Australian which touches on The Billings method. I've heard of the Billings Manual as in "there's a baby in every book". They're in their bassinets, but you get the idea...
Now contraception can be tricky at the best of times - just check out failed sterilization. Unfortunately Billings is contra-feng shui for the bedroom. There's inevitable loss of qi associated with mini-lab installion for saliva microscopy, core temperature recordings and stretch-testing of cervical mucous. A speculum, flexi-mirrored fibre optics, and stirrups bench improves your cervix-spotting hit rate.
If you can stomach sex after all this, bear in mind spit is unreliable, mucous is just satisfactory for the "typical and regular", and the thermometer must be inserted in bed, strictly first thing in the morning. You need to predict signs of ovulation from five days beforehand. Things change fast and those intrepid tadpoles can swim for a week, so it may be simpler to call the astrologer. In the Fallopian tubes no one can hear an egg scramble.
Once you've established you are "unsafe" there's the condom option, but how natural is that? I've never seen a polyurethane tree. Condoms have a failure rate of approximately 11% per annum so pencil-in an annual babyshower within your bookclub circle. Abstinence is somewhat more reliable.
There are days when you really don't feel like it... when you are bloated and snarling with PMT, or when it'll amount to a great bloody mess. Cheer up! Those are the safe days! Tick these on your calendar. Then are times when you're recklessly tempted - to risk fortune and fidelity for a spot of passion. Be warned! These are the dangerous, Abstinence Only, days! Presidents can't hold back, but ordinary mortals are expected to just say no. Cross these days off on your calendar.
Now, thanks to a Dr Eugen Jonas, there's a dark side of the moon. He predicts sex is unsafe on days of the month that correspond to the lunar phase at your time of birth. With the help of a chart (he may sell you one) there are more crosses to mark on your calendar. But remember... it takes two to conceive, so male lunar unsafe days should also be calculated (tricky as sperm is formed about two months before ejaculation, better deny yourselves a few more days).
I'm figuring this eliminates about 20 days per month, which leaves about eight days of playtime. Now subtract the "headache" days of PMT and MT and you're left with a day or two a month of unrestricted, unfettered gametic partytime... if your stars are right!