There are the standard things which if you are writing this I am sure you have already tried. The paints you can put on that taste horrible, tobasco, soap under the nails, etc. So I am guessing you are looking for something a little more drastic.

I was a nail biter when I was young. My mom finally broke me of it when I wanted to start painting my nails. She told me that there was poison in the nail polish so while she wanted to paint them, she couldn't until I wasn't biting my nails. (Yes, I was gullible enough to fall for this too!)

As an adult I found something that is even easier. Nail biting often becomes a habit more than anything else. Artifical nails are a great tool to help break that habit. They also help to give you pride in your hands if you have been hiding them due to your nail biting.

Sometimes I have found that simple is the most effective, and this is the simpliest I have found!