"It's great for the city," says Cox, who has been involved with the event since 1994. "It just shows another step in the recovery."
While it hurt to move the event away from its traditional urban base, the earthquake left a much deeper mark on the marathon.
"The previous race director before my time was Brian Taylor," says Cox. "Brian tragically got killed in the earthquake. He was in the CTV building.
"He's always in our minds. He was my mentor, always in the background when I was organising [the race]."
For Cox, getting the event back into the city is a way of honouring the legacy Taylor helped to create.
"One of Brian's goals was to create an event that would bring Christchurch to a standstill. We were doing that prior to 2011."
And Cox is determined to do it again. Early registrations for this year's event are already high. But that belies the difficulties he and his team have had to overcome in moving the event back from the outskirts of town.
"We knew another two or three years out there would probably start to see the event decline. There was no wow factor, no point of difference."
After the 2011 earthquake, Cox's team were able to scramble to put together an alternative course in Lincoln so the event could still be held. They did so because, even after all the devastation, the people of Christchurch still had an appetite for the marathon.
"After the big one in February we knew we would have to cancel. We had the entry forms with the printer the day of the earthquake, and we rang those guys and said, 'put the job on hold'. We really thought we were going to cancel it, [but] over the next four to five weeks we had people contacting us saying, 'hey, is the marathon still happening?'
"We got together with our sponsor and decided to move it out to Lincoln. We pulled that together in six weeks. It was pretty amazing."
But at that point the likelihood of getting the event back to the city was remote at best, says Cox.
"The council said, 'You'll never be able to hold [it] in the city again. It's too hard. It just won't happen'."
Despite that Cox and his team pressed on, knowing that the event risked petering out altogether if it stayed out of the public eye.
"You need to be in the city with an event like this so the public can watch it and you can really get that atmosphere. I've always said the event is not just the race - it's the people, the public, all the community groups that get behind it. We really missed that support because of where we were."
The hard work and determination has finally paid off, and Cox predicts this year's race could set a record in participation levels.
"Entries are well ahead of what they would normally be at this point. We're miles ahead. It's early days yet, but it's very encouraging.
"It was always my goal [to get the race back to the city]. Our catchphrase, even out in Lincoln, was 'Christchurch, we're back'. I remember calling that out to everyone on the start line and it was an amazing feeling.
"The running community really got in behind us. We weren't going to be stopped by the earthquake."
City start line
What: The Christchurch Airport Marathon
When: Sunday, May 31
Distances: Marathon, half marathon, 10km, kids' event
For more information, visit: http://www.christchurchmarathon.co.nz/