So remarkable is it to find someone who is not stampeding out the door on an early retirement deal that Orkney did a trawl of other education authorities to find out if this was a record. And it certainly is, the nearest challenger being one who has toiled at the chalkface for a mere 32 years.
Dewar, who is 63, must also be unique in having spent virtually his entire career in one post in one school. A couple of years at Montrose Academy and Forfar Academy at the start of his career is all that has come between him and perfect attendance at Kirkwall.
Although his folks were Orcadian, Dewar says he planned to stay just a few years on the islands before moving on. "But, whatever plans you make, events always have a habit of getting in the way," he says.
His main achievement? "Sticking at it for 40 years, I suppose." But his biggest kick is gained from pupils who take up his subject despite all the other alluring bits of the curriculum.
Geography is now a subject under pressure, Dewar feels, as it contends with planners who want it to become part of social subjects along with history and modern studies. "Rubbish," is his considered response. "Whatever happened to the idea that a subject is worth studying for its own value? An amalgamation will give us the worst of everything." But, cheering up, he notes that Kirkwall has a healthy number of youngsters taking Standard grade geography.
Dewar will not be short of ideas about where to spend his leisure time. But, he said, his first plan is to take his holidays when the schools return in August "just so I'll realise I've finally departed".