[JK11]

Hello - I hope someone out there can offer advice, I don't have experience with aggressive dogs.
I have 2 cattle dogs and I just took my friend's Great Pyr 5 days ago as she was having trouble keeping him from running off. She has 3 other dogs. She said he was submissive to the other dogs, all small dogs, at her house and no behavior problems. She purch him as a pup from a breeder who raised him as a livestock guardian. He is 4. We live on a farm. Now he seems to be trying to rid the area of my dogs and particularly seems to be guarding me. He will go after a dog if they are coming toward me or him and stand over it barking aggressively - no injuries - yet! I have started walking him Cesar Milan style and am teaching him basic commands, and using what I know about how to be pack leader. But I need more HELP! When he runs the dogs off, should I bring them back and make him move away? Not sure how to respond to that. I don't think he should be allowed to claim whatever space he wants. He is very submissive to me and when I yell NO! (out of panic) he usually drops to the ground. If I am nearby and i see it start, I just block him and say no and make him sit, then I stand there til he lies down and relaxes, then I say good dog. Am I even in the right UNIVERSE with what I am doing?
Thanks for any advice.