You see, he was a prison guard. That meant of course that he spent over a year stationed at Fort Leavenworth, site of the US military's largest prison. Most folks think only of that when they think of the place.
So the joke is this. Friends would come up to me and say, "So I hear you're son's in the Army."
"Yep," I'd answer plainly.
"Where's he at?"
I would simply say, "Leavenworth."
This would always be followed by a pause as they processed the information. Eventually they would ask, sheepishly, "Leavenworth?" And I would answer, "Yep. Couldn't be more proud of the boy."
There would be another pause as they tried to think what to say next. But after letting them hang for a few seconds I would say, "He's a prison guard. He's on the right side of the bars." It's funny how much relief they showed when I would finally admit whole story. Many of them would audibly sigh when I let the cat out of the bag.
Have I properly thanked you son, for feeding my impish sense of humor?