I teach biology at Hillsdale College.  I use the survey markers to mark trapping grids.  My students and I trap small mammals (mostly native mice) and record demographic data and collect tissue for DNA analysis.  Our grids are usually laid out so that each station (each survey marker marks a station) is 20m from the others.  We place a trap or two at each station.  I will trap 3 – 4 times a year for, I hope, several years.  In the past I have used wooden stakes, but wanted to try something different.  So far we really like the survey markers. They go in the ground easy and are easy to find.   A few were run over by a 4-wheeler and were not broken.