fighting rat terrier females

Question
We have 2 female and one male rat terriers. they are all fixed. the females without warning will just start fighting going for the throat if you will they draw blood almost everytime. we have tried everything. Why are they doing that? and how do we get them to stop? please help!!!!

Answer
When two bitches fight on sight and so severely that blood is drawn, you're well past an easy cure.  This is a struggle for dominance between them.  Perhaps they are close in temperament, or perhaps the wrong one is being promoted by you (the human members of the family) without of course realizing it.  The only possible way to attempt to cure this relationship breakdown is by:
1.  instituting positive reinforcement training, i.e., clicker training
2.  observing body language (after studying what to look for)
3.  determining what dogs are "saying" to one another with that body posture
4.  determining which dog is the most naturally higher ranking (even slightly more dominant)
5.  putting both dogs on Nothing In Life Is Free (NILIF) to demote them psychologically under you
6.  rewarding (click/treat) every subdominant signal (no matter how subtle) the least dominant shows the other
7.  making certain no fights erupt at any time, which may mean feeding separately (in separate rooms), removing toys (if dog is resource guarding), eliminating treats (except for the clicker related reward)
8.  observing the apparent strongest temperament (if you can even succeed at doing this) in regard to her interaction with household members (human) so as to totally avoid rewarding "pushy" behavior in any way
9.  veterinarian may suggest, if you are absolutely certain of what you are doing with behavior modification, hormonal (progesterone) therapy (short term) or beta blocker (truncates fight/flight mechanism) in the CLEARLY subdominant dog.

This is a tricky business.  It requires you do an enormous amount of study and reading and followup 100% of the time (ALL adults in household) for many weeks, perhaps months.  Even then, there's no guaranty.  I could post an hour's worth of instructions here but frankly I've found that most people who ask questions on the internet don't do the WORK and can absolutely make the situation worse.  I suggest you find a professional who can evaluate/assess temperament in both bitches, interview you in depth regarding training and other important human to dog aspects of the relationship, instruct you in how to use a clicker (if s/he determines there's some help available that will stop the problem), how to use NILIF, order of feeding and interaction, etc.  This person must be more sophisticated than many dog trainers so I recommend a certified applied animal behaviorist.  You can hopefully find one in your area at one of the following sites:
http://certifiedanimalbehaviorist.com/page6.html
http://www.arkanimals.com/ark/dg_expert_referrals.html
http://www.animalbehavior.org/ABSAppliedBehavior/caab-directory

You don't mention anything in your question other than the problem behavior.  Scant information makes it impossible to offer advice.  This situation will get worse, one of the dogs will be injured severely or will be killed by the other.  You must act.  Find a behaviorist.