A chance discovery while on holiday in Canada has prompted a borders farmer-contractor to start importing a stone detector that will fit all makes of forage harvester.

Paul Nixon, who is based near Selkirk, saw a forager working happily in Alberta in very stony conditions. When he spoke to the driver he found he was using a locally-made Rockstopper stone detector that could detect the presence of any stone from golf-ball size upwards with virtually no false alarms.

How does it work? When a stone goes in the front of a forager, the sprung-loaded feed roller is designed to jump upwards. A sensor is installed to detect this movement and uses the existing metal detector circuitry to stop the forager’s mechanism and sound an alarm in the cab.

This was of particular interest to Mr Nixon, who had only recently suffered two sets of stone damage to his forager, one costing £8000 in repairs and the other £9000, both in the same season. Not only did he fit the Rockstopper on his own machine but he became the European importer for the equipment at the start of this year. With a total of nearly 60 units sold (many of those in Europe) he is finding a ready market for the simple device.

“A dial lets you set the sensitivity to the size of stones you’re likely to have,” he says. “If you set it to detect stones as small as a golf ball it will work fine but may give a few false alarms. However if you set it for fist-sized stones it will go all day without any false alarms.”

The unit can be fitted in just over an hour by any farmer or contractor.