I love to watch my dogs as they interact, so that I can get a better idea of "dog language". One thing I always do with my aggressive foster dogs, is take a step back, and make sure I am very careful when I give affection. I do not do it around the other dogs, and I watch for dominance signs the whole time. I never really thought about why I did this, until I had a student whose dog was having extreme aggression and dominance, and I knew that she was very very affectionate with the dog. The next day I was watching Riley and Rocco interact, and I saw something very interesting...

First I should start by saying that by this time, Riley had pretty much accepted Rocco as above him on the hierarchy of power in the household (aka more dominant), and so he had stopped trying to put his head over Rocco's back, he stopped trying to body block Rocco from the water, door etc. 

So I was watching Rocco play with Sarah on the floor, he was rolling around, his ears were back (submissive, non threatening ears) and he was trying to talk Sarah into playing with him. Riley came over to see what was going on, and Rocco turned to ask Riley to play too, and Riley immediately went in to dominant mode (his ears went straight up and forward, he head held high) and stretched his head/neck above Rocco in a show of dominance. I took Riley away before a fight broke out, but not before I learned a valuable lesson in doggie language. 

When we get all lovey-dovey with our dominant dogs, they see it as a moment of weakness, and an opportunity to assert themselves as the leader. This is why when you have a very dominant dog, you need to take a step back from all of the over the top affection until they learn and accept their position as a follower in the household. A good rule of thumb is 5 seconds of affection, and only on your terms. You should also make sure your dog does not get on the same level as you; i.e. on the bed with you, on the couch with you, you are the floor with him, etc.