 Coulson was released by Barnsley at the end of the season, leaving him free to join Grimsby permanently, signing a two-year contract on 31 May 2010.In the third match of 2010–11, at home to Hayes & Yeading United on 21 August 2010, he took a kick to his ankle, which was expected to keep him out of the team for a month.He returned on 18 September 2010 after starting in a 2–1 defeat at home to Fleetwood Town, but was substituted at half-time.