Here's a true story my sister told:
She babysat for her best friend's son when he was around 2 or 3. She had no firm guidelines for discipline and would warn, warn, and warn again. This boy would not listen or do what she said. One day, her husband got tired of all the warnings and said to either carry out the punishment or stop warning.
After that, she had a 3-strike policy, which she discussed with the mother and then explained to the boy. She warned once, reminded once with a short time out, and if the time out didn't work, spanked. The poor kid got his share of spankings for a week or two. After that, he never got another, at least not from my sister. That made everyone concerned happy and the mother was so impressed with the change in behavior that she started using the same system.
I believe her method of administering the spankings is noteworthy. She would matter-of-factly remind the boy that he used his chances without raising her voice or displaying anger. When the spanking (3 "wacks" maximum) was over, she would hold him on her lap, reassure him that he was loved, and talk about what led to the punishment.
I'm not advocating beating kids, but that one made an amazing turn-around using that system.