They sell some stuff in pharmacy stores that you can paint on like nail polish and it tastes really awful; that might be a deterrent. Another method people have used is to put a rubber band around your wrist. Every time you find yourself biting your fingernails, snap the rubber band. It hurts, and maybe just making yourself aware of the problem and associating it with pain might help you to stop. A last idea is to get a really nice manicure, which may make you think twice about ruining such an attractive hand by biting. Good luck stopping!