I find that separating them if possible helps - where they cannot see each other at all. I have three, the pup is the Doberman and they want to "kill" the gardener. Fortunately I know approximately what time he comes each Wednesday - so I get up early to feed them, put each of them in a separate room with the door closed and I try not to react whatsoever to their barking. I find that when they don't each have the other two to join their barking party and when I ignore them, it slowly becomes boring for them and they settle down. Before I started separating them my pit mix actually put her head through my dining room window and shattered the entire window (without a scratch to herself amazingly). Also, they used to get so worked up and in each others faces barking that they turned on each other. I found the only solution for me was to isolate them from each other and from the cause - 30 minutes later the gardener is gone and I have a calm, submissive household....without completely losing my sanity.