We have two male dogs (and two females as well), a boxer mix and a lab mix. We've had the boxer for 4 yrs and the lab for 1. The lab showed up on our doorstep, and we adopted the boxer as a puppy. The lab is very well behaved 95% of the time, but on four occasions during the past year, the lab has bitten the boxer, two of the times for seemingly no reason. The other two were when there was food or a toy involved. The boxer is my wife's baby, and I am very fond of the lab. My wife wants to get rid of the lab so that the boxer doesn't have to walk around on eggshells. Plus she was the one who broke them up twice and got bitten herself during the process (once by the boxer and once by the lab).
Also - the lab is protective of our yard and did bite one of our friends when he came in the backyard. I hate to get rid of him, but we obviously also can't have him biting, even if only on rare occasions.