On 18 May 2012, Fenlon signed his first professional contract with the Dons.[2] His first involvement came as an unused substitute in a 3-1 League Cup First Round defeat at Stevenage on 14 August.[3]
On 21 August, he made his Football League debut as a half-time substitute for Warren Cummings in a 6–2 defeat to Burton Albion.[4] He made his first start for the club four days later in a 5–1 defeat at Bradford City.[5] Fenlon scored his first professional goal in a 3–2 defeat to Oxford United on 2 October.[6]
On 6 June 2014, it was announced that Fenlon had been offered a new contract but could not come to an agreement with the club. Manager Neal Ardley revealed the Fenlon was offered reduced terms due to the club's budget situation and, according to Ardley, Fenlon's attitude.[7]
On 26 August, he recorded his first victory for the club in a 2-1 Scottish League Cup win at Stranraer.[13] His final appearance for the club came in a 2-0 League Cup defeat to Hibernian on 23 September.
On 28 November, Fenlon's contract was terminated by mutual consent.[14]
Fenlon made his league debut a week later in a 1–1 draw with Needham Market.[19] Making 14 appearances in all competitions for the Tanners, his final outing came in a 3–1 victory at Hendon on 10 December.[20]
Fenlon scored his first goal in almost five years, and his only for the club, in a 5–1 defeat at Faversham Town on 4 February 2017.[21] He left the club at the end of the season.
On 10 October 2017, Fenlon became the club's first player to score at the Elmbridge Xcel Sports Hub – their new ground shared with Walton Casuals – in a 6–1 Combined Counties Challenge Cup victory against Badshot Lea.[24] Five days later, he scored against from the penalty spot in a 2–0 win at Horley Town.[25] On 21 October, Fenlon scored his third penalty of the season in a 3–3 draw against Balham.[26]
