Substitution therapy is one way you may be able to make some headway in your quest to stop biting your nails. It's a pretty basic psychological idea. What you're trying to do is replace a negative habit with another positive habit. This kind of therapy is used to kick all kinds of issues, but in the case of nails you'll probably get more out of a replacement that involves your fingers. Some of the more common recommendations for nail biting include artsy things like drawing, painting or working with clay. If you don't have an artistic bone in your body, you may want to think about getting a stress ball you can squeeze when you feel the urge to bite your nails. Over time, using substitution therapy can help you stop biting your nails altogether.