And the director of rugby says he would not welcome any approach from the Rugby Football Union (RFU) for his attack coach.
England are searching to fill that role following Scott Wisemantel's move back to Australia after guiding the Red Rose to the World Cup final in Japan.
Vesty is now hot property following his fine work at Worcester Warriors and now Saints.
But Boyd will not be letting him go without a fight, admitting the 38-year-old has been one of his most important recruits since switching to Northampton in the summer of 2018.
"Sam's contracted with us for about another 15 years," Boyd said jokingly.
"Bringing him here is one of the best decisions I've made.
"We were disappointed to lose Alan Dickens to England Under-20s but he'd been here for 11 years and he felt he needed a change, something different to find out what the world is like outside this club.
"We were sad to lose Dicko but when I talked to him about it, I knew it was the right thing to go on his coaching journey. Jake Sharp has stepped up from the Academy (to become interim defence coach).
"One of the best decisions I made here was the coaching group and Sam Vesty is a talented young coach, Phil Dowson is going to be a really good coach and Matt Ferguson is doing a really good job with our scrum.
"We'll sort the defence portfolio out going forward."
When asked what would happen with Vesty if England did come calling, Boyd said: "I wouldn't be releasing him, that's for sure.
"It'd be interesting and I suppose everyone's got their price if it's about money, but I think Sam's a bit more about job than money.
"I'm pretty sure Sam's happy with what he's doing at the moment."
Vesty switched to Saints from Worcester Warriors a year and a half ago.
And Boyd explained: "When I got the job I made the decision I wanted to have English coaches here.
"I went to people I knew and said 'I don't care whether it's a backs, forwards, attack or defence coach, who is the young, up-and-coming, promising English coach?' and all paths led to Sam Vesty.
"I rang him out of the blue and he wasn't particularly happy with his lot at Worcester and he was looking to leave.
"He had some options apart from Northampton so I was very pleased when he decided to come and work with us.
"I'm happy with all the coaches. They're all high potential coaches."
So what is it that makes Vesty stand out?
"All the best assistant coaches have a good eye for the game," Boyd said.
"It's like the difference between a good referee and a bad referee. A good referee sees a picture and knows what's wrong and can interpret what that problem is straight away.
"An average referee will go 'that picture doesn't look right, let me think about it' and by the time he's processed it, the game has moved on.
"Sam Vesty, and two or three coaches I've worked with in New Zealand, immediately their eye tells them what's happened and they know immediately.
"For a technical coach coaching rugby, you have to have technical knowledge and be good at what you do."