While not strictly Corona, i’m looking for some ideas as to how best to achieve a boulder based retaining wall like this?
Boulders from Megascans and Tyflow?
The walls follow a specific path/volume
Depending how long the wall is and how manually you need to tweak it, I would have thought RailClone is the best bet to distribute randomised rocks (from megascans or elsewhere) - you can probably even take one of their presets and amend it to suit a rubble stone wall.
There are even a few examples on the iToo forums where people are asking for similar - example 01 - and - example 02 with decent starting points you could try.
This can be also easily achieved with Chaos Cosmos assets and Chaos Scatter, you will have total control on the spline path by scattering your boulders along with 1d - on splines. Random transformations and avoid collisions will need to be tweaked. If you are looking to achieve the running bond type of placement, I would either suggest multiple spline paths, or a single one but your instanced model should consist of a properly patterned setup of stones.