Has any country tried the single term?

Yes!

Ecuador and South Korea have “no reelection” in their constitution.

Costa Rica has just one 4-year term.  But since 2003, the President
can run for reelection after being out of office for 8 years. The term
limit is one of the elements for giving Costa Rica a stable
government.  
LEARN MORE

Mexico, right after the Civil War, copied the Confederacy.
President Vicente Fox Ouesada is in for that single 6-year term, and
then out forever. If the first Constitution of Mexico had that single 6-
year rule, Mexico could today be the third most prosperous country
in the world.  
LEARN MORE

 Amending the U.S. Constitution would encourage other countries to
do the same.

      To LEARN MORE about an universal mandatory single six-year
term for the Heads of State in all countries of the world,
see www.6-year.com
1 Six-year Term for U.S. President
OTHER NATIONS