Any suggestions on getting my boy to stop biting his tail

My little guy (age 10) has bit the base of his tail for his entire life, since he was a kitten. He essentially always has a nasty scab and I feel bad for him. I’m not sure if it’s because he’s bored when we’re not home or what. He’s an indoor kitty only and we’ve been to the vet several times over it. They think it’s a behavioral thing (orange boy) because they’ve said it’s not fleas. They did prescribe some meds for anxiety and we tried giving them to him but he thinks he’s in trouble lol. I’ve read some things about using bitter sprays but I worry that some may not be safe for kitties to lick. Would any of you happen to know of any that are safe for my son? (Or any other suggestions of course!!)