My Dogs Sudden Violent Behavior

Question
I have 2 male neutered golden retrievers that have been buddies and have stayed together in the same big fenced in area for about 5 years now, however, yesterday, for some reason, they were violently aggressive toward one another for the first time we have ever seen.  I was afraid that they would kill each other.  They have never done this and I am afraid for one or both of their lives now.  Can this behavior be explained and what can I do?  Thank you!

Answer
I cannot explain the behavior without seeing them in person, Shane. It could have been caused by just about anything, from dominance, to possessiveness, to redirected aggression from something outside the fence that they were both barking at. I would suggest that you not leave the two boys alone together, inside OR outside, until you can consult with a professional behaviorist and/or trainer who can come to your house and observe the two of them interacting.