In Mark. Gooley wrote:
Likewise bits of concrete slabs, if you don't mind the look, or
stone or brick from wrecked buildings. Again, there's the weight.

One trick I've heard of for purpose built concrete edging is to paint it
with a mix of yoghurt and water soon after it's laid. It will stop
looking like new ugly concrete and start looking like aged mossy stone
in next to no time, according to the tale.

Hmm, not sure. I'd avoid using fruit yoghurt :-)