A husband leans over and asks his wife, "Do you remember the first
time we had sex together over fifty years ago? We went behind this very
tavern where you leaned against the back fence and I made love to
you."
"Yes," she says, "I remember it well."
"OK," he says, "How about taking a stroll around there again and we
can do it for old time's sake?"
"Oh Charlie, you old devil, that sounds like a crazy, but good idea!"
A police officer sitting in the next booth heard their conversation
and, having a chuckle to himself, he thinks to himself, I've got to see
these two old-timers having sex against a fence. I'll just keep an eye on
them so there's no trouble. So he follows them.
The elderly couple walks haltingly along, leaning on each other for
support aided by walking sticks.
Finally, they get to the back of the tavern and make their way to the
fence. The old lady lifts her skirt and the old man drops his
trousers.
As she leans against the fence, the old man moves in. Then suddenly
they erupt into the most furious sex that the policeman has ever seen.
This goes on for about ten minutes while both are making loud noises and
moaning and screaming. Finally, they both collapse, panting on the
ground.
The policeman is amazed. He thinks he has learned something about
life and old age that he didn't know.
After about half an hour of lying on the ground recovering, the old
couple struggle to their feet and put their clothes back on.
The Policeman is still watching and thinks to himself, this is truly
amazing, I've got to ask them what their secret is.
So, as the couple passes, he says to them, "Excuse me, but that was
something else. You must've had a fantastic sex life together.
Is there some sort of secret to this?"

Shaking, the old man is barely able to reply, "Fifty years ago
that wasn't an electric fence."