Here's yer chance to stop nail biting.
Get a set of buffers--this is a set of nail files that have an emery and finer emery ending with a leathery sort of buffer. Some kinds of buffers come in a single block with the buffer and smoother on each side, and you can get them at Sally's Beauty Supply or any similar type of place, even the drug store. They do not look girly and in fact, buffing is good grooming if you are a guy. (No polish needed.)
Start by evening out your nails. Then buff (you use the roughest part of the smoother on the nail surface, then another finer one, finally you buff to a shine.)
WHY? Well, the buffing brings blood to the nail bed and stimulates growth (so does sunlight, so a vacation in Hawaii is in order, however...the budget!) After a month of keeping your nails in order, you will have a small white part on the tip for strumming and you will not be biting because you won't have any loose bits to gnaw on and your obsession will have been redirected to buffing. Meanwhile, keep carrot sticks around for crunching on something to satisfy the oral part of the habit.
When nails are smooth and groomed, the impulse to bite is reduced. Whenever you feel the urge to gnaw, pull out the buffer and bring up the shine again and grab a baby carrot. Trust me, this will work. I keep my nails short even though they grow like weeds because my main instrument is a piano. I have to compromise with a eighth-inch length which is all I can stand on the keys (my master class teacher didn't want to see ANY white but she ain't around so ...) The buffer smooths the tips and really helps for strumming, the buffing adds thickness eventually to the nail for strength.
Give it a try.