It is a first for the Balclutha-based meat processor, which celebrates its centenary in 2012, meaning Mr Denston has been employed there for more than half the life of the entire plant itself.
It was a fact not lost on the company's management, who were very proud and awed by such loyalty.
At least two other Finegand staff are in line for the same milestone within the next two seasons.
He is one of two long-serving Otago employees to achieve 50 years' service.
Dunedin bindery assistant Anne Lillie, at Rogan McIndoe Print, also joins the club.
Mr Denston (66) has noticed almost as many changes in the industry as he has seen sheep.
And the wily stockman has seen more than his fair share of animals in his half-century effort.
His time at the plant has coincided with a boom in killing numbers.
In the seasons up to and including the 1958 season - when Mr Denston first wandered on to the site - a total of 13.69 million stock were slaughtered and processed there.
In the 50 years since, the number stacks to a shade under 96 million..
"Just a coincidence, nothing to do with me," Mr Denston said, laughing.
But his workmates say he is not only part of the furniture at Finegand but one of the best workers they know.
Plant manager Graeme Stanbury said it was a "phenomenal achievement", especially because he believed there would be very few workers reaching such a milestone as the meat industry changed.
And changes there have been.
Mr Denston and a small gang of up to three other workmen would kill sheep by hand.
One would grab the animal while another would swoop from behind and slit its throat with a sharp knife.
The knife, after several kills, would be dropped into a bucket of cold water and wiped clean before the killing resumed.
Not exactly hygienic but effective, Mr Denston said.
Good luck with trying to get away with that kind of technique today, he noted.
For years, he and his gang would work in the one area - "I reckon I didn't move more than six feet (2m) for years" - but at other times, Mr Denston's abilities and knowledge were used in different parts of the plant, most notably at its on-site farm where he and his trusty tractor are still a familiar sight.
Technology might have changed the way the animals were processed, but the"brotherhood" remained and the memories were something he said he would always have.
"I never get sick of working here. They might get sick of the sight of me, though."
He fondly refers to a photograph taken of him back in his first or second killing season.
Wearing his trusty black singlet and with a full head of hair, it is a world away from life at Finegand today.
"If you stay here 50 years, look and see what happens to you," he said.
He recalled many fond times, most not fit to print, he said.
Friends, and workmates like "Hurricane Harry" who used to run around the plant like a madman but claimed to all and sundry he was "nothing more than gentle breeze", spring to mind.
Others he was less keen to "dob in", but good times were had, he said in an assured tone.
Mr Denston is a careful workman and is proud to say he can recall only two accidents.
Two cuts to his hands in 50 years was not a bad record, he said.
As for his future at Finegand?His days there were numbered, he said.
"My legs are getting quite sore and I've knocked off 50 [years]. It might be just about to time to call it a day."
Six other long-serving PPCS Finegand staff were presented with 30-year service awards this week.
They were Bruce Graham, Brian Bell, Greg Ayson, Maureen Willis and Peter Rhodes, while the late Gay Ngawaka received her award a few days before her death recently.
For her part, Mrs Lillie (65) was trying to keep her achievement under wraps.
Regarded by management as "the grandmother" of the company, she has spent the last half-century working in a job she did not originally want.
She was not sure what kind of career beckoned when she left school at the age of 15 but it was not meant to be one in the printing industry.
"But look, 50 years on and here I am," she said yesterday.
After serving a four-year bindery apprenticeship, Mrs Lillie was still not keen to stay but slowly began to enjoy the role, the challenges and changes in printing over the past five decades.
"Technology changes everything in printing just about every five minutes," Mrs Lillie said.
Her career also saw her rise up the printing and manufacturing union ranks to national vice-president four years ago.
But as for her time at the Dunedin printer?"Good times, good memories, too.
"They say I'll still be here when the lights go out," Mrs Lillie said.
