Dave, if you're in Scotland, you can't be too far from a freshwater loch. Assuming you can get to a freshwater loch, then the skies the limit. Make sure you disinfect the rocks first with aquarium disinfectant and then throughly clean them off. Better still, if you know where your water source is, then taking rocks/stones from there won't alter the hardness of the water. Just a thought. I know when I was staying at Bala in Wales, my friends had a tank and built his aquascape from the local rocks at the lake. Lovely place and a lovely tank too.