You have to hand it to David Kennard. One day he's a farmer suffering in patient poverty as all small-scale farmers seem to have to nowadays - and the next? Video producer, and soon to be well known author. No small feat that.

How on earth has this happened? How can one man - and his dog - beat the system? Well it's the canine that is key. David started out as shepherd. It's all he ever wanted to do in life, and he loves his dogs. If he loved them, he reasoned when farming seemed to be going belly up, maybe others would too. So it was that the farmer decided to make a film. He'd show them doing what they do best - working.

David farms in one of the most beautiful spots in the country, north Devon. And Morte Point, an area of land he leases from the Trust to graze his sheep is more beautiful again - wild, steep hillsides, sheer drops of cliffs to the ragged sea below, black heads of seals bobbing in the swirling tides. It is perfect, and a wonderful walking spot, and it's his sheep that help keep it that way. Morte is a Site of Special Scientific interest, but without the grazing provided by the sheep, it would soon get taken over by bracken and gorse and this spiky, spectacular headland would be impassable.

The food chain is delicately poised here, and the 150 ewes chomp away doing a good job for the Trust, while the dung beetles that follow them are an important part of the diet of kestrels and peregrines and a lot of small mammals such as voles and shrews. Some rarer species at the Point include the ground mottled grasshopper and black banded moth, and odd flora like Autumn squill and Rock sea-lavender.

For David, it's a kind of heaven on earth, and he admits that a favourite part of his working week is the time he takes to round up the sheep using his dogs, Greg and Swift. And this is where the magic comes in. Seeing the way these sheepdogs move together is like watching some ancient mystery at work. Immediately, their personalities shine out as you watch the way they reel about the sheep, always one step ahead, the calm proficiency of their movements like something that has been choreographed.

'Greg is a freethinker,' David explains. 'He's the brains of the outfit: he realises for himself exactly what needs doing. Swift is more intense, and she moves with incredible precision. She needs more commands from me, but together they are a fantastic team.' Whatever the weather in the smugglers' country, with its heavy sea-mists and soft rain the dogs love the work. 'They don't just love it; it's then only thing,' says the boss. 'It's what they live for.' He knows the dogs so well he can almost predict their every move.

With a system of whistles - a different set for each dog - he controls each movement, each whirl of the back, each crouch. They move across the rough ground at around 35 miles an hour, he reckons, doing the job - these days there are 800 sheep, compared to the 270-odd a shepherd might once have had - that even 20 dogless people would find hard to do. How does this mystery work? What's it all about? 'It's in the strength of their eye.' David says, enigmatically. Looking at the dogs, their oats gleaming with health, eyes sharp with a hunter's hungry gaze, you suddenly catch a glimpse of what he means. Sheep can spot a weak dog, and once they have, they will ignore it.

There are others on the farm, but not every dog will be as sharp, reliable and focused as Greg and Swift. Gall for example, is in a world of her own. Although on a good day she is better with her 'eye' than almost any other dog, she is moody and has serious off-days. The team have their own pecking order, with Greg at the top, and any puppies of course right at the bottom. All of his has already fascinated the public. People have been buying his video in droves. David, who shot it himself, asked 'Vet' actor Christopher Timothy to do the voiceover, and then schlepped it around all the major distributors. It was worth it: the video sold more than 50,000 copies, and a new DVD will be soon be launched.

It is a remarkable achievement: the professionals would find this kind of project difficult, let alone a one-man band with a serious day job. It's only a theory, but it may be that this soft-spoken, totally unassuming man has succeeded so well because no-one can bear to let him down. His persuasive talents are such that he is even in the Avon catalogue, a fact that has given his friends a few belly laughs, but has sold his video to an entirely new audience. Out of blue, the publisher Headline has snapped him up, and when his new book comes out in March, his conversation-friendly story will reach thousands.

Swift - as good-looking a dog as you could hope to meet, with a particularly good right profile and a definite sense of her own beauty - will accompany her master on some of the book signing, perhaps doing the odd doggie paw print autograph. Right now, David is training a new pup, Jake of whom he has high hopes: 'It's an indefinable quality, something to do with the way he weaves between the sheep, the way he concentrates and shows no fear.'

It's a dog's life, stardom. But then, someone has to do it.