Which number is missing?

A couple married thirty years were revisiting the same places they went to on their honeymoon. Driving through the secluded countryside, they passed a ranch with a tall deer fence running along the road.
The woman said, "Sweetheart, let's do the same thing we did here thirty years ago."
The guy stopped the car. His wife backed against the fence, and they made love like never before.
Back in the car, the guy says, "Darling, you sure never moved like That thirty years ago, or any time since that I can remember!"
The woman says, "thirty years ago that fence wasn't electrified!"