The cache is not hidden at the published co-ordinates, these are for the car park in Carlops.
This is a bonus cache which can only be solved after successfully completing the Carlops / Leum na Caillich Adventure Lab. If you have successfully completed the AL, the cache co-ordinates can be found in your journal (specifically for the "Carlops Drinking Fountain" stage of the lab cache).
You may either walk to the final co-ords from the village car park, or you can drive to GZ. Please do not move stones in the wall, it is not necessary in the hunt for the cache.