By this time, Mr. Fox had risen to the rank of sergeant in the Royal Electrical and Mechanical Engineers and announced his retirement from the sport. However, his coach Ron Bright persuaded him to continue. In the 1972 Munich Games, he achieved the best individual placing by a British pentathlete up to that point, finishing fourth. He went on to win team gold at the 1976 Montreal Olympics alongside teammates Danny Nightingale and Adrian Parker.
Mr. Fox retired from the Army in 1983 as a captain. He then turned his attention to eventing, successfully competing at Badminton and Burghley on a mare named Finisterre, which he had purchased for £400.
In 1997, he became chairman of Pentathlon GB, continuing to significantly impact the sport. He was also active in Pony Club tetrathlon. In recognition of his contributions to modern pentathlon, he was appointed MBE in 1974 and OBE in 2000.