The plastic tie wrap is an excellent idea. Following your footsteps or observing the drag marks of a sand scoop simply tells you the direction you traveled and any variance from a straight line.
Having that plastic tie on your search coil, especially centered on the coil, shows you your search coil sweep pattern. This lets you know if you are overlapping efficiently throughout the entire side to side sweep-route. To me, it's much better to know which way the search coil actually traveled to produce the best possible coverage and good–target recoveries, instead of which way the human traveled.
Too many times I see people working a beach or any area really where are they walking at a faster pace and the search coil is not covering the entire area efficiently. We go hunt places to find stuff, not to take a stroll. This morning I'm going to add a dozen or so plastic ties to my accessory item tote that travels with me just to be prepared for such a site search. A very nice idea .... and affordable, too!
Monte