3. An ex-pen or a crate
You can't be everywhere at once, but your dog probably can. Unless you live at the top of a mountain, and are eagerly awaiting the day your groceries are delivered by drone, at some point you're going to have someone come to the door. And you're going to have to open it. Worse still, you may even have to invite them in!
I don't know about you, but my relatives are not the most compliant people on the planet. It doesn't matter how many times I tell them not to stare at, reach towards, or otherwise annoy my reactive dog, at some point they're going to do it anyway. So, to protect them, my dog, and my own sanity, I use an ex-pen. When the takeout guy arrives, the ex-pen goes around the door. When I have guests, I can separate their half of the room from the dog's.
A crate would serve this purpose just as well, so long as your dog doesn't see it as a punishment. Just having people in their space is bad enough for many reactive dogs, without the added insult of being put in a time-out. Make the crate a wonderful place to be, however, with something to chew and a soft place to doze, and maybe having guests over won't seem so bad.