Having sweeped some area with a magnet already to find sharp stuff harmful to grazing animals: rather unpractical because either you need a ridiculously strong

Having sweeped some area with a magnet already to find sharp stuff harmful to grazing animals: rather unpractical because either you need a ridiculously strong magnet (to the point it becomes dangerous to handle it, moreover in areas with ironstone it attracts huge amounts of tiny debris), or it needs to be only a cm above the surface. And not all screws and nails are magnetic.