Watch your ass

I'm not trying to be vulgar, but I really do want to know... What's the origin of "Watch your ass?" A friend told me it goes back a couple hundred years to when people were put in the stocks in public as a form of punishment. Supposedly, if you didn't have someone to come out and "watch you ass" for you, you could be molested.

I would have thought being molested was a fairly minor worry for anyone sentenced to spend time in the stocks - or more likely the pillory, as in the stocks the victim was seated.

People thus punished didn't just get a few rotten but soft tomatoes (or whatever) thrown at them; anything that the baying crowd could pick up and hurl was used, including stones. It was also common for their ears to be nailed to the structure to prevent them moving their heads.

DFG