Length of Contracts

It is understood that a team can sign their own player for a max of 8 years, and an outside team can sign a player for 7 years during Free Agency. It is also understood that team can re-sign during a player's last year in a contract to an extension. What is stopping teams from signing a player for a 1 year contract on July 1st, and turning around July 2nd and offering them an 8 year extension, effectively making their contract a 9 year contract?