The Mapsurfer, who is like internationally competitive in the sport
of Orienteering and should know, advocates including a "calibration
leg" in your clues. This would be a paced off distance between two
easily found spots before you get to the tricky find-the-tupperware
part. Done well, this would show how your paces relate to the
placers. (Not that we've done this well ourselves...we use "steps"
but try not to do it where it would be confusing....)

Jay in CT