A couple of points to make:
1. It's impossible to place the cache on public lands because no such land exists! Every square inch of these islands is owned by someone - there is no such thing as "Public Land". Even National Parks are merely administrative areas - the government only owns military land through the MOD.
2. Here, everyone sets their GPS units to OS Grid. Ordnanacy Survey is the government department which has mapped the British Isles. Everyone I know sets their units to OS and leaves them unless going overseas. So I've given the cache these co-ordinates.
NN42606 / 24542
It is level 5 difficulty. This is the hint: drive and hour and a quarter North of Glasgow, and then hike up a steep hill for another hour and a half. Follow a series of stream into a shallow corrie, and as the ground steepens, look to the right (South) for a large rock marked by a small piles of stones placed ontop. The cache is underneath the large rock.