An Englishman and a Frenchman stood at the Pearly Gates awaiting St. Peters judgement. St. Pete looked in his register and was amazed - he found that both had been the least sinful to approach the gates in over ten thousand years. He decided that to reward them he would grant them each a wish.
The Frenchman considered this for a time and decided that he wanted nothing for himself but would like to benefit future generations of Frenchmen. He asked St. Pete if it was possible to erect a huge wall around La Belle France to keep out the filthy English with their BSE and Foot and Mouth disease.
St. Pete congratulated him on his lack of any personal greed and with a snap of his fingers the wall appeared.
The Englishman considered this carefully and asked "I'm very curious. Please tell me more about the wall." St. Pete explained, "Well, it's about 150 feet high, 50 feet thick and nothing can get in or out."
The Englishman quietly said, "Fill it up with water."