I was in a rush earlier... Sky was a tailbiter. He stopped when I put him in a high traffic area (he sees us allll dayyyy, while we're here, and watches us constantly... he's looking at me right now, rofl). Every time one of us moves he wiggles around and watches. He's like a dog, haha. So yeah, that's what helped him, but every fish is different. :\
Addendum: Other things that have fixed tailbiting include more decor (silk plants) and re-arranging decor frequently. Some bettas will play with a floating ping pong ball. An airstone might entertain him for a few hours a day. Or he might hate it. Make sure he doesn't have too much current jostling him around, as well.
Tailbiting is awful! >_<