He coached international crews from New Zealand, Switzerland, South Africa and Great Britain to success at World Championships and Olympic Games.
[3][4] After graduating, he began teaching at Melville High School, and joined Waikato Rowing Club.
The failure of the eight to repeat that success in the 1984 Summer Olympics led to Mahon being gradually excluded from the New Zealand coaching setup, and moving to Switzerland.
He was diagnosed with colon cancer in 1997 and, despite being given only months to live, continued to coach with some success for four more years, also running the London Marathon twice during that period.
[5] In the 1984 New Year Honours, Mahon was appointed an Officer of the Order of the British Empire, for services to rowing.