Fill it up!
 

One day, an American, Frenchman and an Englishman were walking down the beach having a peaceful conversation. The Frenchman stopped his blabbering about almighty France and pointed to a lantern sitting in the sand. On it was the paining of a golden genie. And out popped a golden genie with golden bracelets, necklaces and even earings.
"I'll grant you each one wish," the genie explained.
"I want 'Merica to forever fertile, ya know, for my crops," the American said. And America would be forever fertile.
"I wanz a big wall around ze precious France so no one will get in," the Frenchman asked the genie. And a big wall was built around France.
"Please tell me, explain the characteristics of France's wall," the Englishman asked. The genie explained how big and thick the wall was.
"About 150 feet high and 150 feet thick."
"Okay, thank you chap. Fill it up!"