So when the opportunity arose for him to spend a few months working in the Solomon Islands, he jumped at the chance.
Leaving behind a young family in Oamaru was a wrench but, as he said, there was never going to be an ideal time.
He had always wanted to serve his country overseas, like his father, who was in the air force, and he went with the support of his wife Sue.
Det Duncan, who turns 43 on Friday, headed to the Solomons in September and arrived home on Christmas Eve - a very special Christmas present for his four children.
Thomas (10), Jack (6), Millie (5) and Harrison (16 months) thought they were going to Oamaru airport with their mother to pick up a friend, only to discover it was their father.
The three weeks had been "fantastic" and he leaves tomorrow to fly to Brisbane and then on to the Solomons on Thursday.
He will return home permanently after about eight weeks.
Det Duncan, who has worked in the Criminal Investigation Unit in Oamaru for the past eight years, has been involved with auditing police stations in the Solomons, as part of a project to help re-establish the police force.
He was keen to get back and finish what he was doing as he could see the improvements.
He was involved with looking at everything from exhibits - which were often "in a mess" - to how officers processed prisoners and looking at dockets [known in New Zealand as files] to see if crimes were being investigated properly, as well as the standard of statements.
On average, about 45% of dockets were missing, so the public was not being served very well.
That was not a criticism of the police but how much the department had broken down over earlier tensions, Det Duncan said.
There were some very good police officers, but they just needed their systems back up and running, he said.
He went by helicopter to one police station where there was thick mould on the ceiling, the roof leaked, there was no electricity or running water and a solar panel was used to power a truck battery to run the radio.
Riot gear consisted of metal helmets from World War 2 and wicker shields.
Det Duncan said he was trying to make the most of the experience - "it's a matter of immersing yourself" - and would return home with a different outlook on life.
