Folks have been detecting for over 60 years, you're basically talking about re-inventing the wheel. There's a reason we make plugs with knives or trowels, they work, and if you pinpoint well you don't damage any targets. Not to mention the weight of carrying around a drill with enough torque for the job and an auger which would potentially damage targets. Lots of old timers use and used a thin brass rod with a handle to probe for targets without damaging them. Most modern detectors have a pinpoint mode which work very well when learned, and the "DD wiggle" works well on detectors with DD coils which most VLF detectors use these days. To pinpoint with many PI detectors you turn the coil sideways and scan twice at 90 degrees with the edge of the coil. Takes some practice but works when learned.