[Irravepem]

Pills are the most effective form of anti-conception, but the main question is if you can trust her to take them at the right time and keep a clear head once she misses one. As long as she takes them regularly(!) and doesn't have stomach problems or take antibiotics, you'll be fine. Well, at least I am for over one year with my current partner.

PS (only just seen Steve's post): Pre-ejaculate has not been proven to be the cause of pregnancies, so I wouldn't worry about that.