Before the 2004 season began, Toronto Rock head coach and GM Les Bartley announced that he would not be behind the bench for the upcoming season due to his battle with colon cancer, and assistant coaches Ed Comeau and Derek Keenan were promoted to interim head coach and GM respectively. However, after beginning the season 2-4, Comeau and Keenan were fired, and Terry Sanderson was hired as the new GM and head coach. Sanderson turned the Rock around, guiding them to a 10-6 record and first place in the Eastern Division. They lost to Buffalo 19-10 in the division finals. During the off-season, Sanderson made a blockbuster trade with GM Johnny Mouradian of the San Jose Stealth, acquiring his son Josh, nephew Phil, and Rusty Kruger for fan favourite Steve Toll, Darryl Gibson, two draft picks, and a player to be named later, who ended up being goaltender Anthony Cosmo. Any cries of "nepotism" were silenced during the next season, as Josh set a new single-season assists record with 71, and the Rock finished 12-4 and in first place in the Eastern division for the seventh straight year. They defeated the Rochester Knighthawks in the division finals, and then beat the Arizona Sting in the Championship game, held in Toronto, to win their fifth NLL championship in seven years. Former coach and GM Les Bartley died the day after the Championship game. 2006 was a disappointing season for the Rock, finishing with their worst record ever, 8-8, and losing to Rochester in the division semi-finals. Less than two weeks after the end of the regular season, Sanderson was fired.
2007 and beyond
Sanderson worked with his brother Lindsay once again during the 2007 season. Lindsay, the head coach and GM of the Philadelphia Wings, hired Terry as an assistant coach. Both were relieved of their coaching duties after the season as the Wings missed the playoffs for the fifth consecutive year. On July 17, 2007, Sanderson was hired by the Calgary Roughnecks to be their defensive coach for the 2008 NLL season. On June 10, 2009, after two seasons in Calgary, including the 2009 championship season, Sanderson was re-hired by the Rock as their new GM and assistant coach. On November 13, 2014, Toronto Rock owner, Jamie Dawick, announced that Sanderson would be taking an indefinite leave of absence from his role as General Manager, with Dawick serving as the interim General Manager in his place.
Death
On November 27, 2014, Toronto Rock owner, Jamie Dawick, confirmed, via Twitter, that Sanderson had died due to health issues.
Personal life
Sanderson owned and operated Sanderson's Source for Sports, a hockey and lacrosse equipment store located in Orangeville.