Englishman, Australian & Frenchman

An Englishman,Australian and a Frenchman were all shipwrecked on a desert island whilst wandering on the beach they found a strange bottle when the Australian picked it up a huge genie popped out and said i would normally grant 3 wishes but since there are 3 of you I will give you one each.

He asks the Australian what is your wish

I am a cattle man from the outback and love my country and wish for it to be forever fertile the genie said it is done.

He then asks the Frenchman what is your wish I love my country and I don't want to share it with anyone else please build a wall around France to keep everyone out except Frenchmen. The genie said it is done

He then asks the Englishman what is your wish he thinks for a little while and says I am quite content and cannot really think of anything I need however this wall how big is it the genie replies it is 150 foot tall and 50 foot thick

Aha said the Englishman now I know what my wish will be. What is that said the genie

The Englishman replied with a smile " fill it with water"