Get a gel manicure
One of the classic pieces of advice for biters is that they should paint their nails. The logic is that if they look nice, you'll be less likely to bite them. Polish often does act as a deterrent, but since aesthetics aren't exactly at the root of the habit, lots of people just end up biting it off, along with their nails. That's where gel manicures come in. Products like Shellac and Gelish are extremely hard and thicker than polish. Biting gel off is difficult, and the texture is different enough to snap you out of your biting pattern if you do put them in your mouth.
Tape 'em up
Sometimes a little Scotch Tape is really all you need. Putting a small strip of tape down the length of each nail isn't noticeable, but even dedicated biters are put off by the sudden sensation of having weird crinkly stuff in their mouths. Not only does it make you notice that you're biting, but it also begins reconditioning you against the experience.
Keep your nails short
This might seem counterintuitive, but lots of biters are able to quit in bursts and then start again worse than before. The problem is that they grow their nails out over a few weeks, then end up biting off all the new growth and then some because long nails are much easier to bite off. Instead, keep them trimmed to the very tips of your fingers so that biting causes noticeable effort and is easier to avoid.
Source: Flickr user Akiko Photography