I have bitten my nails most of my life. The No Bite may work for some, and it's relatively inexpensive, but be aware that a persistent nail biter will bite regardless of the bad taste, since they already bite regardless of the pain. I would suggest you try the No Bite, or equivalent, but also pay attention to when he bites his nails. For me, I tend to bite my nails when I'm feeling stressed. Your son may be using nail biting as a way of coping with stress, he is more than likely not fully aware that he is doing it. If you see him biting his nails, instead of telling him to stop (because he won't) quickly engage him in an activity to distract him from biting, preferably something where he will have to use both of his hands, also take some time out to help him relax and destress. You may also want to try placing gloves on his hands (out of sight out of mind). I have also found that chewing gum helps with the oral fixation and the need to chew.