Goalkeeper Mark was signed in February 2012 - as a free agent he was permitted to put pen to paper outside of the transfer window - and provided cover for Steve Simonsen for the remainder of the campaign ahead of being highlighted as his potential successor.
He began his career with Arsenal but never made a senior appearance, instead making his name north of the border representing Aberdeen, St Mirren and Falkirk. Latterly he represented Blackpool and made four appearances for them before moving to Bramall Lane, initially on trial, before agreeing a two and a half year deal.