Nah, after a year, you would have dead gators all over the place.
A 300 wide and 300 foot ditch will work. It can be built, there isn't anything that can't be built.
It is absolutly amazing we can erect the Statue of Liberty in the 19th century, we can build the Panama Canal with steam shovels, we can build the world's tallest building during the start of the depression and with hand set rivets - the Empire State Building, we can build both the Hoover Dam and the Golden Gate bridge, we can destroy Germany and Japan and then rebuild all of Europe and parts of Asia but we can't build a border to protect our country.