I have also had to deal with this. Recently I started taking more supplements, specifically magnesium in lotion form, iron, zinc and calcium and stopped biting my nails for the first time in forever. I have read that nail biting may be a mineral deficiency, it seems to be the case for me, give it a shot.
I will look into this more, but for the last few months I haven't used any other products or paid any attention and it has just stopped but will come back mildly when I forget to supplement for a day or two. I will continue to supplement as I'm not getting enough through my diet and the results are wonderful, I just keep forgetting to do it every day, must build a habit I guess.