New Young Female Dog Attacks My 13 Year Old Male?

It sounds like the corrections you are doing are pretty on the ball. I wouldnt resort just yet to prong collars and choke chains (sorry I think they are overused and used as a replacement for training, despite the TD's I will get...Ive worked with big dogs my whole life, some with various aggression issues, and have never needed any of that so I find it odd that people use them as often as they do). I do somewhat agree with another poster who suggested that it may not be the right time to bring a new dog into the house as it can be really hard on older dogs but if you are willing to work at it then keep up what you are doing, build up the respect factor (no food or going outside or coming inside etc without doing something like a sit first), keep the new dog leashed in the house for quick corrections and if you are at a loss, find a dog trainer in your area who is comfortable with aggression issues (not just obedience) and have one or two sessions so her can observe and offer advice.