I have a tail biter too, whenever he gets stressed he bites his tail. Your best bet is to keep his water exceptionally clean, to avoid infection, and keep his environment as stress free as possible. Some people also suggest new silk plants/ornaments to distract them and keep them entertained, but that's never worked with my guy, worth a try tho i guess.
3) random trigger biting- basically there's no constant as to why they bite
If you can figure out the cause it is easier for us to suggest what may help him. Tail biting is frusturating. Believe me, I rescued a biter from my teacher a year ago and he has steadily kept biting and regrowing for a year now. My last ditch effort is to put him next to a female which I'm doing tonight...I've tried EVERYTHING!
I honestly don't know how to entertain a fish.. and he really doesn't have room for more plants or anything in his little 1 gallon tank =//
I'm setting up a 10 gallon but I don't want to put him in there yet cause I was treating him for what I thought was fin rot. Now i'm guessing he was biting his tail
I guess I could move my female over closer to him for now. see how that works