Johncock was leading the club champion award early in the 2005 season before breaking his leg in a game against Melbourne in round seven. He had spent most of these games in defence, but was occasionally pushed forward. He missed a large chunk of the season, but returned before the finals and played a couple of games. He was hampered in the finals, however, by a leg injury.
In recent years, Johncock has been playing mainly as a defender, teaming with fellow indigenous player Andrew McLeod in running the ball out of defence. This was enough that he was named as a back pocket for the Dream Team in their clash with Victoria during 2008. Johncock did make a brief return to the forward line late that same season, as Adelaide desperately searched for someone to replace a host of injured forwards.
It had been rumoured that he wanted a change of team for 2009, but after the 2008 AFL Draft he confirmed he wanted to stay at Adelaide.
Johncock played his 200th AFL game in 2011, but Adelaide were humiliated by St Kilda to the tune of 103 points. Playing on Stephen Milne, Johncock had eight goals kicked against him.
Johncock retired on the 1st of July, 2013, saying his body could no longer withstand the rigours of AFL. Though, he has expressed interest in playing out season 2013 with the Port Adelaide Magpies in the SANFL.