Spanking should only be considered if a verbal lesson would not work
Then what exactly are they learning in that case? Kids are not stupid - they can always be reasoned with.
I wouldn't dream to claim I've never been angry or frustrated as a parent but in my experience it is far more effective to reach them on an emotional level than a physical level.
We must have done something right as we have two fantastically respectful and well-behaved, empathetic kids and when they were young we've been out at restaurants and had old couples come up and say how well behaved they were and how nice it was to see.