Fairfax, VA. - George Mason University wrestling head coach Brian Shaffer has agreed to a three-year contract which carries through the 2002-03 season.     Shaffer is in his sixth season at George Mason and his ninth overall as a head coach. He has a 43-20 overall mark with the Patriots (69-40-1 overall). He guided George Mason to back-to-back Colonial Athletic Association championships in his first two seasons in 1996-97, and the Patriots have placed third, second and second in the past three CAA Championships.     During Shaffer's tenure, 16 George Mason wrestlers have qualified for the NCAA Championships. Sophomore Donnie DeFilippis, currently ranked eighth in the nation at 141 pounds, became the fourth Patriot freshman under Shaffer to qualify for the national tournament last season and placed in the top 12 at 141. Senior Sean Shea (1996) and DeFilippis (2000) each have been named the CAA "Rookie of the Year" and a Freshman All-American by Amateur Wrestling News under Shaffer's guidance, and Shea was the "Outstanding Wrestler" at the 1997 CAA Championships.     "We're pleased to be able to offer a lengthy contract to a quality coach like Brian Shaffer," said Tom O'Connor, Assistant Vice President/Director of Athletics. "He has proven he can produce winning teams and outstanding student-athletes, and we feel giving him this security will help continue to strengthen the program."