Fenwick received a four-month prison sentence in September 1991 after being convicted of drink-driving. He served two months of his sentence.
Fenwick scored all 8 of his league goals for Tottenham from the penalty spot in just one season, 1988–89. After 1990, it gradually became clear that Fenwick had witnessed his best days as a footballer. He was sent on loan to Leicester City before getting a permanent move to Swindon Town, a newly promotedPremier League team. His first season, 1993–94, saw Swindon winning only 5 games of a total 42, conceding 100 goals and being relegated. Fenwick played 26 games during this season, and was noted for breaking the leg of Paul Warhurst. He played only two games the following season, was released, and ended his playing career shortly thereafter.
Following in the footsteps of many former players, Fenwick decided to try a managerial career. In 1995 he replaced Jim Smith as manager for Portsmouth. After an underwhelming first full season in charge, where the club only avoided relegation on goal difference, an improved second season saw the club miss out on a play-off spot by just one place, and they also eliminated then-Premier League Leeds United from the FA Cup. A dire third season cost Fenwick his job however, and he left with the Club bottom of the Division One table.
In a quite remarkable turnaround of events, Fenwick was canvassed by an Asian businessman and coerced to become the new public face of beleaguered non-league outfit Southall between 2000-2001. It led to fellow Queens Park Rangers team-mate Mike Fillery being installed to take charge of first team affairs, before both were ousted amid the debacle surrounding the Club's ownership.
Fenwick's next manager job was at Northampton Town in 2003, where he only lasted for 7 games. His first game saw a 1–0 lead turn into a 2–1 defeat away to Blackpool. The next five games saw just two draws and three more defeats. His last game in charge was against Bristol City. The 2–1 defeat saw calls for his departure from fans and he left the post the following Monday. He was replaced by Martin Wilkinson. That summer, Fenwick was lined up to become the new manager of Luton Town, but he decided not to take the job due to uncertainty over the Club's ownership - amid allegations of fraud surrounding Hatters, and former Southall chairman John Gurney.
After enduring a fairly torrid time with Southall, through no fault of his own, Fenwick transcressed to become director of football at Ryman League side Ashford Town (Kent) in 2004. Yet, despite plans to reshape the Club for bigger things, a lack of private investment and on-field success, meant the Club was unable to move forward.
Since his managerial days in England, Fenwick has spent a considerable amount of time in the Caribbean nation of Trinidad and Tobago, which he has enjoyed a great degree of managerial success - winning the country's professional football league on four occasions (2002, 2003, 2007, and 2008).