I found this out the hard way when putting together a small pond on my allotment. I never planned for needing so many rocks for the shelves/ borders.

Not having a car at the time made acquiring them challenging to say the least. (Not to mention the gravel for the bottom). Still, I left no stone unturned and eventually ended up repurposing some of the local stones used for landscaping (which now have purpose!)

I think acquiring the damn rocks took up about 90% of the build time!

Your neighbour did you a real favour.