Teaching doesn't suit everybody, but he liked it.
"Teaching taught me a lot as well.
"I enjoy watching people grow to whatever belt they decide to go to. It's definitely a boost for people who are lacking in confidence."
As a fifth degree black belt and Shihan he is the top teacher at Whanganui's Zen Do Kai dojo in Trafalgar Pl, and also teaches others from lower North Island centres.
It takes years to move beyond a black belt toward the red belt worn by a full 10th degree Dan.
Anyone beyond black belt status is likely to be "on the path of the Warrior" and will " unwittingly change their way of life, for they can never be the same person again", the Zen Do Kai website says.
The Whanganui dojo has about 30 students of all ages and both sexes. One 65-year-old man has just achieved his black belt.
Anyone of any shape and size can come and have a go, Leathem said.
"People have this idea that you have to be fit and flexible. But you start with a white belt and progress through the different colours.
"You learn how to stand, how to throw a punch, how to throw a kick. Each colour has different aspects."
The Zen Do Kai martial art is about street situations where self defence is needed. But Leathem can't recall any of his students using it on the street.
"To me it's more about teaching people that they don't have to use it. I don't like bullies, arrogant people.
"It's quite often better for people to walk away than to use it."
Students pay for their classes, and the money goes into renting the hall and paying expenses.
Leathem works full-time for Pacific Helmets and he doesn't want to turn his martial arts skill into the kind of business where he would have to seek out students.
"I want people who want to learn."
He's at the dojo two evenings a week and often at the weekend for training, gradings or just to clean the place.
His next grading may have to be judged by someone higher ranked and from overseas. It will be based on what he gives back to the system by teaching and holding events.
He's not showing any sign of letting up.
His Zen Do Kai commitment is unpaid and Garland said it needed acknowledgement.
"I would really love to give him a wee nod, from myself on behalf of all the people he has guided and mentored over the years," she said.
