Suddenly his ears were assailed by the snarling and barking of an apparently ferocious Doberman Pinscher. The rep turned tail and fled 60 yards to the road.
'Eventually, he drove back down the drive and stayed in his car for a long time before venturing out,' Mr Yarnold recalls with a chuckle. 'When you're confronted with a sound like that, you don't hang around.'
The idea was conceived after a chance conversation at this year's Royal Show. 'We were showing off our bird scarers when somebody heard a dog bark. He said we ought to get that noise on tape to frighten off the burglars. I took his name and address, and six weeks later we had a working prototype.' Four months after that, the barking Doberman was highly commended in the innovations section at the Smithfield Show.
Now the Yarnolds are faced with a dilemma. Do they continue to grow gradually without borrowing? Or do they capitalise on the demand for a hot product by having the alarms made in bulk by a manufacturer, who would require advance payment?
'I only buy things when I have the money,' Mrs Yarnold says. Business has expanded steadily since she started making bird scarers on the kitchen table with the help of a pounds 500 Enterprise Allowance, after being made redundant three years ago.
'We couldn't eat off the table for two years,' she says. 'I used to work from eight until two the following morning. Our daughter, Vicky, would help out, and Rob would join in when he finished his other job (in sales and marketing for a radio company).' Six months ago, he decided to take the plunge and join his wife full-time.
Martley Electronics, as they call their business, has now moved from the kitchen table into a small unit in a business centre just outside Worcester. They employ a staff of one. Turnover this year is expected to hit pounds 200,000. Last year, it was pounds 87,000 and the year before that pounds 58,000.
'We took nothing out of the business for the first 18 months,' Mr Yarnold says.
'Every month we set a target, and every month we exceeded it. We bought all the products of our competitors, checked how they worked and thought of ways of improving them.'
Both the Yarnolds have farming backgrounds. Their electronic bird scarer mixes the distress calls of a number of species, including rooks, lapwings and black-headed gulls.
'It sounds like an amplified space invaders machine, but it certainly clears the fields,' Mr Yarnold says. He goes out with the sort of tape recorder used by BBC reporters.
How did he get the Doberman to perform?
'I just stood round the corner from the yard of our local pub and held out the microphone. He's a vicious bugger and you wouldn't want to get too near him.'
The bark is now selling for pounds 249, plus VAT. But this is the sort of guard dog that does not need feeding, does not make a mess on the drive, and never sleeps.Reuse content