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.  
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Mexico, right after the Civil War, copied the Confederacy.
President Vicente Fox Ouesada was 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.  
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 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