The dog was about to invade my safe zone
That may be, but I want you to prove in a court of law that a dog invading your safe zone constitutes a deadly threat. Then I want you to think about the aftermath when the owner comes running towards your safe zone. Are you going to shoot him and his little dog too? Certainly the laws have made it easier to avoid prosecution and the burden, in many places, now lies on the state but I think you are advocating risky behaivor from two points.
1) You have many options as an adult to deter a dog, shooting it should be the last choice. You aren't a child anymore, you shouldn't limit yourself to that line of thinking.
2) Most people are not good enough shots to hit a small dog running full speed at them with a compact pistol equipped with iron sights at night.
#2 is the key point. You may be the next Rob Letham, but even he misses swingers sometimes and he is a better shot than most people in the world. Even a larger dog, I'll spot you a boxer or a lab, full speed at night when you are still breathing hard from running, I'll wager a case of beer that you couldn't hit it 1 time in 10 in a vital area under the said circumstances.
My main point is that you are advocating putting rounds into the air in a public space over a "safe" zone. Maybe that is "the way you roll" but I disagree with that advice. The original poster has a lot of options open to him, shooting is, IMHO, one of the worst in his situation. Your safe zone, as you call it, means nothing in court. I can stand 1 inch from your face and scream that I want you dead but until I actually take action to make it so, you cannot use deadly force to stop my behaivor and expect to sail through a review by the DA. Texas, like most places, has a specific set of circumstances that allow deadly force, a safe zone is not described anywhere within those laws.
Lastly, it is your obligation to talk, not confront, with the owner about the dog. It is due diligence and will pay off later when you decide to kill his dog. At least your attorney will have something to throw out there in your defense. I'm not telling you to be his friend, but a simple conversation can avoid a lot of problems. For all you know, he might put his dog up and if he doesn't, there are other options that are safer overall than shooting the dog.