It all depends on your own Betta's personality. Some can be brought out of it with some decor rearrangements, a bigger tank, a smaller tank, tank placement (next to another Betta or farther away from another Betta) and sometimes exercises with a mirror can help but sometimes no mirror at all can also help.
My Veiltail had a longer tail but he I think got angry being next to another Betta's tank (the other Betta was somewhat blind so he never reacted to any war dancing) and he started biting his tail down to a specific point. That was about 2 years ago, every time his tail grows out past that he bites it off again, it doesn't seem like it's an aggressive thing now because he isn't constantly chasing after it but I think he likes it shorter.
I had an amazing looking HM boy who I think also got mad at the fact he couldn't actually attack the Betta near him. He would flare and go crazy then turn and rip his tail off. I have photos of him down below when is tail was still long and he first started biting then at the length when he stopped and let it start growing out a bit. It was very unfortunate because he was such a pretty boy. I tried moving him by himself in a room with no other fish at all, I tried putting him next to some females, giving him different kinds of tanks and decor and nothing at all worked. This mainly happened when he was much younger, so it might have been an adolescent issue since that was around the same age as my VT, but I don't know. He eventually stopped but I think that was because he couldn't reach his tail anymore because it was so short. He unfortunately had to be put to sleep for other reasons (severe Lymphocystis you can see starting in the middle of his tail) but I was never actually able to get him to stop biting when he had his pretty tail.
I have had one successful bout with tail biting though. Another HM, he was fairly young when he started and I had him placed next to a very aggressive CT male, they both would occasionally flare and what not, eventually the HM got fed up and started biting. I put a barrier up between the two and that stopped it for a little while, eventually he found a way to where he could still see the CT and would go nuts. At that time he was in a 3 gallon, he was also growing like a weed so I moved him into a 5 gallon and he's completely stopped. He's been in his 5 for about 6 months now and he hasn't even looked at his tail and he's building nests off and on and he's very much more chill. :)
Last edited by TheCheese909; 01-11-2013 at 08:26 PM.