My idea for a LDEF (Long Duration Exposure Facility) on Mars' surface would be a non-returning mission, just to clarify the concept a little more...

You would have several motors and a Geiger counter inside some bearings and various fabrics and materials expected to be used on Mars on the outside and placed it in contact with the surface. A balloon which touches down at night or a rover with an arm might do the trick. Would need a system to check the integrity of the fabric and materials while being tested. Possible a microscope and an abrasive wheel to view the weave and to aid the wearing of the materials, etc.

If we got creative with the design maybe make it be an artificial snake and it crawls around while...