Lab chases her tail viciously til bloody

Question
I have an adopted 3 yr old lab that becomes very aggressive towards her tail. She has a 6" tail and our vet believes she probably bit/injured it so it was cut. She snarls, shows her teeth and gums and sometimes foams at the mouth which chasing her tail. It is the most vicious behavior I have ever seen. Nothing stops her when she is in this mode. Cloricalm worked for a while, but not anymore.

Answer
This is an issue for a qualified animal behaviorist.  Ask for a referral from your nearest vet college, or from your own veterinarian.  The Animal Behavior Society should have listings, too.  This is a serious "stereotypical behavior" and should be dealt with by a professional.  You may also want to show your vet or behaviorist this information: http://dsc.discovery.com/news/2009/03/24/dog-tail-chasing.html
One vet suggests using an Elizabethan collar in conjunction with drug or behavior therapy: http://www.wolfweb.com.au/acd/tailchasing.html
This page does not start out on a hopeful note, but there are some links at the bottom that may be helpful to you: http://home.frognet.net/~footloos/khi.html