Bad behavior will occur but it is how it is responded to that means the difference between extinguishing the behavior for a moment or for a lifetime. Punishing the bad behavior may stop it in the moment, but will have fallout and often the behavior wasn't addressed so it reappears. By redirecting or ignoring, and rewarding for good behavior you are creating lifelong results.
If I see a puppy or dog chewing on a sock or shoe or other item they should not have, I first remain calm. I find something the dog absolutely loves, like a ball, a frisbee, a filled kong, or even a bit of chicken or liver, and show it to them. At this point the dog will eagerly come to get the proper item to chew or look up from what they are doing.
If they move away from the item, I would use a marker word such as YES! or GOOD! or if I have my clicker, I would click for the right behavior moving away from the item. They would then receive a better reward and I would retrieve the forbidden item and put it up.
If they just looked up from the item, I would go into game mode and toss a handful of treat either up and to the right or to the back of the dog. As they run to get the tasty treat, I would simply pick up and put away the item. Once they come back to me I would click and give a proper chewie or acceptable bone.
To add to the above, looking for the dog to look at and move away from items would receive high rewards, therefore rewarding for good behavior. This makes the behavior strong and the dog simply knows which items to leave and which are theirs to chew. Teaching positive impulse control, attention, recalls, and other skills are done in the same way.
Yet, it is seemingly hard, and one of the hardest things to teach clients many of whom are so attached to dishing out punishment. Many still insist on getting a tug on the leash in, or a loud NO! or STOP IT! or rush forward to grab the dog or puppy by the collar. It is human nature. Rewarding doesn't always come so easy when the focus is on "what is that dog doing now?"
What is the hardest skill to train that you've found? Answer as either as a client or a trainer and please embellish on the why.