Boxer Agression

Question
We have three boxers 2 males (4 y/o and 3 y/o)and 1 female (2 y/o).  All dogs are spayed/neutered.  We adopted the female a year ago.  Recently she has become aggressive towards our 3 y/o brindle.  Two times she has attacked for no obvious reason.  When she attacked and we seperated, she charged back to attack again.  Other than these episodes they get along fine.  They eat together, play together and run together.  She has not attacked our oldest boxer.  The brindle usually sits still as she attacks until we get her off of him or he tries to run.  Any advice on what we need to do?

Answer
It's hard to say really without seeing what's going on.  The first step would be a veterinary exam just to be sure there's nothing physical - hypothyroidism, for example, can sometimes cause aggression and is common in Boxers.  If that all looks OK, then you need to think about some behavior modification.  Two years is still adolescence for a Boxer, so she may be 'feeling her oats' and trying to establish her place in the canine pack.  If you aren't currently doing training with all three dogs, that's something to start as soon as you can - 5-10 minutes per dog, a few times a day will do a world of good.  Patricia McConnell has a booklet called "Feeling Outnumbered" which has a lot of good information on dealing with multiple-dog households.  You can also try a Nothing in Life is Free (NILIF) protocol, to reinforce your status as the One who Controls the Resources (and thus Makes the Rules).  There are several articles on NILIF, but one of the originals is here:
http://k9deb.com/nilif.htm

Another Patricia McConnell book along the NILIF lines is "How to Be Leader of the Pack and Have Your Dog Love You For It".  Both are available at www.dogwise.com, among other places.

If the behavior continues, or escalates, you'll want to consider calling in a qualified behaviorist, who can take an outsider's view of things and is skilled at ready dog body language, and should be able to give you some insight into why she's attacking the male.

Good luck!!