I have a 3 year old neutered male cat that attacks his tail as if it belongs to someone…

I am sorry to hear that you are having issues with your cat. Without seeing your male, it's hard to be able to know for sure what to suggest. Your veterinarian is in the best situation to offer suggestions on your cat's treatment, but you could talk to him or her about using a behavioral medication like Clomipramine (it works differently than Elavil and has been used in some cats with success). In other cases, tail biting can be pain related even if x-rays are clear. Often tracing back these cats may have had a tail injury in their past. Some of these cats may get relief from pain medication like Tramadol or Gabapentin. You could also consider consulting with a veterinary behaviorist to see if they can help. Good luck and hope you can get this under control with your cat.