How to punish aggressive behavior in dogs.?

This is what I do, and have been. doing with my dog since he was 8 weeks old. I: grab one front paw, and one back paw(on the same side) and flip him on his back. I then hold him still and say "NO! Thats naughty!" and then i act dissapointed in him and dont pet him or anything until he looks like he gets it. its very helpful, and it doesnt hurt them. Its just a way of letting them know that your the alpha, not the dog, and you have control over him or her. Hope I helped!