During his career Mensing has played for 10 different clubs, including spells with Wimbledon in England; Stenhousemuir, Clyde, St Johnstone, Motherwell, Hamilton Academical, Greenock Morton, Raith Rovers, Livingston and Airdrieonians in Scotland; and Atlanta Silverbacks and Carolina RailHawks in America.

Mensing became a huge fans favourite, with his aggressive style of play and was given the nickname "Gunter" due to his German roots.

[1] Mensing moved from Motherwell to local rivals Hamilton Academical on a three-month loan deal in September 2007, after finding it difficult to progress beyond being a squad player.

[10] He was named captain of his new club on 10 July 2013,[11] and scored a penalty on his competitive debut on 3 August 2013 in a Scottish Challenge Cup match against Berwick Rangers.

[12] Following a serious knee injury Mensing failed to hold down a regular place in the Livingston team, and was released from his contract by mutual consent on 30 January 2015.

[13] On 27 January 2015, Coach Gary Smith bolstered the Atlanta backline with the signings of Mensing and fellow Englishman Paul Black.

[15] After leaving Carolina RailHawks, Mensing signed for Scottish League One club Airdrieonians on 27 January 2017, in a deal until the end of the 2016–17 season.