I feel your frustration. You cannot argue with faith. There are some masterful arguements on this site, one most memorable regarding the flood...wish I could find it again. In the end, you could see the only defense was "I believe..."
What jgnat said about find one point and directing it toward the natural mind is excellent. As much as your mind is spinning about facts, I have found it effective to address something that reaches out to their emotion or feeling, sense of injustice. You never know what will stick.
Good luck.