I have a 2 year old Male English Chocolate Lab named Bear who weighs about 70lbs and a 1 1/2 year old Female Great Dane, Bella, that weighs around 100 lbs. They have grown up together. They play very rough, and because Bear is an english lab he is very stocky, so Bella can do whatever she likes to him without hurting him.
Until recently, they have had no problem playing with other dogs. We would try to take them to dog parks very often. As we sooned realized, dogs form packs and chase and pick on some other dogs. When we moved in to our apartment complex and starting taking them to the dog park, Bella and Bear would gang up on other dogs. Bella could outrun any of them and usually knock them down because she loves using her paws. Recently, when Bella and Bear have been playing and they have a lot of energy, once the other dog is knocked down bear bites the other dogs neck (just the skin), but does not let go. Even when the dog whimpers. We have to get our hands in his mouth and try to pry him off. None of the dogs are ever growling or have their hair all tuffed up, and after we separate the dogs they still are wagging their tails and very playful.
We try to discipline him and show him that that behavior is unacceptable, but it keeps happening. They both LOVE other dogs, but Bear switches some flip and goes too far. This might be ridiculous, but could he be mad that he is always being picked on by Bella, and wants to be the dominate dog for once?
Any help or tips or any ideas on why this is happening would be great!