Three guys -- a Canadian farmer, Osama Bin Laden, and an American Engineer -- are walking together one day. They come across an antique lamp and a Genie pops out of it. "I will give each of you one wish", says the Genie.

The Canadian says, "I am a farmer, my dad was a farmer, and my son will also farm. I want the land to be forever fertile in Canada." Pooooof! With the blink of the Genie's eye, the land in Canada was forever made fertile for farming.

Osama Bin Ladin was amazed, so he said, "I want a wall around Afghanistan, Iraq and Iran so that no infidels, most particularly Jews or Americans can come into our precious Islamic state." Pooooof! Again, with the blink of the Genie's eye, there was a huge wall around those countries.

The American engineer says, "Before I make a wish, I am very curious. Please tell me more about this wall."

The Genie explains, "Well, it's about 5000 feet high, 500 feet thick and completely surrounds the country. Nothing can get in or out -- it's virtually impenetrable."

The engineer says, "Fill it with water."

The height to width proportions are all wrong. I write this as an engineer..

As my sister says - What do engineers use as a contraceptive?

Their personality.