Gravity (you jump up and down after sex, gravity pulls the sperm out)
Mountain Dew as a spermicide
Withdrawal (he pulls out and spills outside)
Doing it in a pool so that the chlorine kills the sperm
Prayer (God wouldn't let me get pregnant)
Greenhouse gases: Any gas that, by an accident of chemistry, happens to absorb radiation of a type that the Earth, by an accident of history, would like to lose.
The internet is like a herd of performing elephants with diarrhoea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind- boggling amounts of excrement when you least expect it.
Why isn't "going through the back door" an option?
Fun fact: There was a heretical sect of Christian Gnostics who believed that only the spiritual world was good and the material world was evil. They were known as the Bogomils, and rumor at the time had it that, because they believed the material world to be evil, then bringing a new life into this material world was a sin. So they engaged in sex practices that would not allow for conception. So it is from the Bogomils that we get the term "buggery."
Homosexuality sounds like it works well.
"All mankind is of one author, and is one volume; when one man dies, one chapter is not torn out of the book, but translated into a better language...No man is an island, entire of itself...any man's death diminishes me, because I am involved in mankind; and therefore never send to know for whom the bell tolls; it tolls for thee." - John Donne
"To waste, to destroy, our natural resources, to skin and exhaust the land instead of using it so as to increase its usefulness, will result in undermining in the days of our children the very prosperity which we ought by rights to hand down to them."~ Theodore Roosevelt (Message to Congress, Dec. 3, 1907)
You guys are all forgetting the easiest method by far.
Who shall ascend the hill of the Lord? And who shall stand in his holy place? He who has clean hands and a pure heart, who does not lift up his soul to what is false, and does not swear deceitfully. Psalm 24
"True law is right reason in agreement with nature . . . Whoever is disobedient is fleeing from himself and denying his human nature [and] will suffer the worst penalties . . ." - Cicero