What would it take to convince a faithful person that god doesn't exist?

This is a counter question to one posted by The Truth entitled "What would it take to convince an atheist that there is a god?" In my experience, this is a vey difficult excercise and I am very curious to hear from religious people on this subject. And please be honest. This is a very interesting area of discussion and I encourage everyone to have a look at The Truth's conversation as well.