Just a week before the September 7 race, when most runners will be tapering off, Sutton will be contesting the 100-mile (160km) Great Naseby Water Race.
''I shouldn't be doing it [the marathon]. But it's a local event and I feel I just have to support it,'' he said.
Last year, Sutton astounded many by running back-to-back marathons on the day. He left from the finish line on Watson Park before dawn, and reached the start line at Harington Pt 3hr 10min later.
He had just 10 minutes to spare before lining up in the actual marathon, finishing in the top half of the field.
For many, the final 10km of a marathon is the moment of truth, and Sutton feels he is no different, despite having longer mileages under his belt.
''It's that last wee bit that still gets you,'' he said.
His advice to potential marathon runners is to be familiar with the distance and adjust the pace to suit.
''The speed that you start out at should be the speed with which you finish. You should try an keep an even flow all the way through. That's the sign of a good runner.''
Sutton ran for the Ariki club in his youth but then focused on rugby, and did not run competitively for 17 years.
Concerned by his escalating weight, and getting encouragement from workmate Malcolm Giles, a member of the Caversham Harrier Club, he dusted off his shoes.
Now, Sutton has completed no fewer than 39 events of marathon distance or longer. He also leads a weekly group, including younger brother Darryl, that goes for a run and then gathers for a debrief and some refreshments.
''It's about the fun aspect to training. That's what it is all about,'' Sutton said.
''The great thing about running is that I tend to always come back with a story to tell. I may have seen somebody, found something or seen something funny. Every run has its story.''
Sutton tackled the Longest Day section of the Coast to Coast earlier this year, with no previous experience of the event.
Another Coast to Coast is on Sutton's to-do list, as is a fourth Challenge Wanaka ironman in January and a fourth Northburn 100 in March.
Entries for the Dunedin Marathon close on Monday. Late entries will be accepted until September 7, the day before the race, but incur a $30 late fee.
Glenn Sutton
Marathon man
Age: 39.
Occupation: Joiner.
Family: Married to Julia, children Emily (11), Ruby (8) and Lucy (5).
Northburn 100: Sixth, 2011; first, 2012; fourth, 2013.
Great Naseby Water Race: Third, 2009.
New Zealand 100km championships: Third, 2012.
Challenge Wanaka: 2009, 2010, 2011.
Coast to Coast: Longest Day, 2013.
Kepler Challenge (60km): Six times, best time 6hr 18min.
