He moved to Middlesrough in 2001 following the appointment of Steve McClaren and in 2003 he was appointed as the team's defensive coach. Harrison took on a more general role after Gareth Southgate took over, but left the club in July 2008 after suffering health problems in recent years. He has since recovered from his health problems and on 22 May 2009 he took up the role of assistant to Chris Coleman at Coventry City. On 4 May 2010 Harrison was named caretaker manager of the club after Coleman was sacked, returning to his role as assistant manager on 20 May with the appointment of Aidy Boothroyd as manager. On 14 March 2011 he was again appointed caretaker manager, following Boothroyd's sacking.