Have you tried Avon Super Shock eye-liner gel?
I'm in love with it, it works amazingly for the waterline, it is so dark and stay forever!
When I first heard about this product I wanted to have it so much. Sam and Nic from Pixiwoo were using it (and still) especially for the waterline. So then I decided to get it too. It was love at first time! such a dark and resistant eye-liner, I cant live without it!!!