The San Francisco 49ers will keep their offensive line intact after agreeing to a three-year contract extension with right guard Mike Person on Monday.Person, who was due to become a free agent later this month, is now under contract through the 2021 season. Though the 49ers didn’t announce the contract’s finances, ESPN’s Adam Schefter reported that Person landed a three-year, $9 million deal that features $3 million in guaranteed money.”Mike earned the respect of everyone in our building for the way he battled through injury last season to start all 16 games and perform the way he did,” San Francisco general manager John Lynch said in a statement released by the team.”Aside from his toughness and durability, he brings tremendous versatility to our offensive line, and we look forward to his contributions to the growth and development of that unit. Mike is exactly the type of person and competitor we look for, and we are very happy to have gotten this extension done.”Person, 30, had started just 18 games in his first seven NFL seasons before starting every game last year.A seventh-round pick by the 49ers out of Montana State in the 2011 NFL Draft, Person never got into a game in his first stint with the team, subsequently ending up with the Indianapolis Colts, Seattle Seahawks, St. Louis Rams, Atlanta Falcons, Kansas City Chiefs and the Colts again.He started 14 games for the Falcons in 2015 and four for the Colts in 2017 among his 59 career NFL games.