Useful research tools: metal detectors!

What is the best way to permanently mark a specific location on the golf course without damaging the turf or disrupting golf? We have found that metal washers, (1/2 inch hole diameter fender washers) buried about 2 inches below the turf surface are easily detected by a good metal detector, but are otherwise invisible. This system has been invaluable to us when setting up research plots and is also useful for following the progress of a patch of moss, a…