Number one when training the dog should be on lead, and you should not have to chase him. Two, if the issue is when he is off lead then a training collar (shock) needs to be used so that he cannot outrun correction. All of my Rottweilers have had to spend some time with the e-collar. What I mean by consistency is if you give a command that is not obeyed then correction comes without exception. You have to speak to them in their language. Treat them the way the pack would, shake them by the scruff of the neck till the scream. I had a friends American Bulldog that was very aggressive, and he did not know how to deal with it. After week I told him to let her loose. She lunged at me a few time without me moving or showing any fear, which confused her. Then she stiff legged up to me with an aggressive posture. I let he get close again, and I grabbed her by both cheeks and bit her right on the nose until she screamed like a puppy. After that she never misbehaved around me again. In fact she jumped on my lap every time I came over. She just needed to know my place in the pack, and more importantly her’s.