Spare the rod, spoil the child.
I will be spanking my child -- unfortunately not in public, since that gets you arrested these days.
I remember the good ole' days, when, as Jeff Foxworthy notes, the only real reason to go to Wal Mart was to watch people spank their kids.
My father spanked me. He would say "you did x,y, and z wrong, and I am going to spank you for it. It is your punishment, and wrong things get punished." Then, I'd get to pick out my favorite switch or belt.
Explaining it and being completely reasonable is the important part.
I simply think that at a certain age, kids respond better to immediate painful/embarrassing (and embarrassment is a BIG tool -- and a proper one) than they do to either emotional guilt-rendering or long-term consequences (e.g. no TV for a week, grounded to your room for 2 days, etc.). Now, after a certain age, I think spanking becomes less of a tool, and these other long-term consequences work better. But, when they're young all they understand is a good whack on the buttocks. MHO.