The southwestern US is being over run with illegals, Florida is being over run with alligators, and they still haven't completely fixed New Orleans since Katrina.
SO....:
1. Dig a moat the entire length of the Mexican-US border.
2. Use the extra dirt from the moat to fortify the levees in New Orleans.
3. Fill the moat with the excess alligators from Florida.
Problem Solved........
