Here's what I really want to stress to you guys: Training really needs to take place outside of "the heat of the moment." The heat of the moment is when your guests are walking through the door and your puppy's jumping all over them. It's when you accidentally drop a sandwich on the ground and your dog runs over to grab it. It's when you decide to go hiking with your dog who hasn't been on a leash in two years because he pulls so hard. It's basically any time when you realize that your dog either hasn't been trained how to do something, or training is failing at that moment for whatever reason.
What do you do in the "heat of the moment"?
First, honestly, usually, if you end up in a situation that your dog has not been trained for and doesn't know how to do, there's not much chance it will end with the dog doing what you want. There's no "magic" tone of voice you can use. There's no magic cookie or magic training tool. Here's what you do instead. (Let's take the leash pulling while you're trying to hike example, just to make things consistent and easy.)
1) Decide if you can remain in the environment, or if it would be better to just leave. If you don't want to struggle through a 5-mile hike with your dog pulling on-leash...don't. Just admit you made a judgement error in bringing him, and go on back home.
2) Look into any possible management tools you have available to you. "Management" is not the same as training -- but it's helpful in that at least you can get through your situation in the easiest way possible, and also that you aren't accidently rewarding behaviors you don't want. In our hiking example -- do you have a no-pull harness in the car? Is it legal and safe for the dog to be off-leash? Doubling the leash over the dogs chest can provide a calming and slowing effect for many dogs.
3) Is the situation so dire that heavy handling is called for? (The "Because I Said So"/ Personal Power techniques are only for worst-case scenarios and not for long-term use.) Heavy handling loses its power when used too often or in place of regular training, and can also disturb your relationship with your dog. In the hiking example, I would not use heavy handling to navigate my dog on a pleasure hike. But I would if two miles in my hiking buddy needed medical attention and I had to go for help. ("Hiking buddy in need of medical attention" is dire. "I drove all this way and bought a forest pass" is not dire.)
4) Do you have capacity and desire to make this into a training session, instead of whatever it was you were originally planning for? If you are able and willing to decide that today's hike was originally going to be a Training Myself for Mount Hood Summit hike, but instead you're going to switch it to Training Dog for Calm Polite Hiking hike, then you can do that. But only if you are truly able and truly willing (i.e., with no resentment) to shift your priorities and put your dog first.
5) This is the most important: MAKE A PLAN NOW on how you are going to address your dogs weaknesses and fix your situation. You can also ponder what exactly went wrong -- maybe, for example, all your leash-walking practice has taken place on sidewalks and that just didn't translate to natural environments. Maybe you never did enough wildlife distraction work or scent distraction work. Maybe your dog has always equated wild areas with total off-leash freedom and now he doesn't understand that he has to be on a leash.
What you *don't* want to do is:
1) Yell at or punish the dog; if he is having a training failure it's most likely that he's just not had adequate training. You can figure this out. Next time will be better.
2) Let the dog continue the unwanted behavior. This is just making the problem worse, and will long-term be even harder to fix!