em An occasional well-deserved smack never hurt any one. What damages a child is either frequent and/or excessive smacks, or being whacked for something they did not know was wrong. They know perfectly well when they have pushed you too far and won't hold it against you if you reacted once.
My usual path when mine were playing up (three fairly close in age, so a certain amount of aggro would surface, and of course they were not always little angels anyway) went something like this.
(Usually step one was enough, unless they were feeling stroppy, when I had to go up a notch. Occasionally we had to go to "final warning" but only very very rarely to the Ultimate Sanction (I could probably count on one hand the number of times) but they knew that I did not promise anything I did not deliver, either good or bad.
First step - (Reasonably but firmly) "Stop that, you know it is dangerous/selfish/ dirty/not allowed/making me deaf" Reason given, unless it is absolutely obvious why it should not be done. Physically remove them from temptation, if they are light enough.
Next step - (More firmly, but not screeching) "I told you already, now stop that" (Remove the thing which is causing trouble. They may be bored/hungry/thirsty/tired. Do something to counter that. Suggest some other game or occupation. Distract them. )
If I was busy, and they were not being very bad there might be another telling before reaching the next step.
Final warning - (Showing that I was now getting rather cross) "I have told you twice already. I am not telling you again. The next time you (do whatever) you will get a smack. (Separate them. Keep a close eye on the main perpetrator and find everyone something else to do.)
Ultimate Sanction - While they are still doing the forbidden thing I administered a short sharp slap to the fat part of the leg. No more warnings, they've had enough of those. If you must punish, the gap between crime and retribution needs to be as short as possible, so that it is closely linked.
No rantings and nagging, no saying they are wicked (it is the behaviour which is bad, not the child) no casting up their misdemeanors for days afterwards. and I kept a lookout for the next good thing that they did and praised it so that they felt like a good child. This was as important as the punishment. demonstrating to them that it paid to be good, and did not pay to be antisocial.
All of them have turned out to be confident and independent adults, not cowed or inhibited, so I seem to have got it right.
Any smacking at all is frowned on these days, but there are other "Ultimate Sanctions" that can be applied. just make sure that they are applied consistently, and seriously, and apply lots of TLC when they learn from the experience and behave well.
"Hate the sin, love the sinner"