Martyn Pollard wrote:
I need to extend a garden by about 10ft, which currently drops down a
steep embankment to a lower level 12ft below. The width of the garden
is about 20ft.

I could just dump tons of rubble down there, but then I will end up
with a slope. I wanted to construct something which would retain the
rubble to create a steeper drop.

An initial idea was to create a retaining wall by stacking 'grab-bags'
which contained a dry mix of aggregate. I would do the mixing and
loading with a mini-digger. I could then backfill with the rubble.

Building a retaining wall with bricks would be another idea, but I
think it would work out more expensive in terms of materials and
labour.

Any other suggestions?

There's a name for nets containing largish stones that eludes me at the
moment. You may have seen them on motorway embankments. Possibly
expensive, but an idea non the less...