We live in the west of england and part of our back garden is a 100 year
disused sandstone quarry, surrounded by mature woodland, at the foot of
large hill with a similar angled unstable slope to yours. Elms had grown
abundantly to about 20' and succumbed to the Dutch disease. We cut them
down, removed the diseased tops and branches and burnt them. Then we laid
the trunks horizontally behind conveniently placed 2' high stumps,
occasionally driving in stakes, so that a flowing flattish spiral (can you
picture that?) terrace follows the line of existing rock outcrops up to a
top outlook. We then backfilled with loose surface rocks and topped off
with the leaf mulch and black topsoil. Planting is traditional with some
water features being introduced.
We dont expect either the stumps or trunks to last forever, but hope (!)
that when they decay, the landscape will have compressed and stabilised
with the help of the new root systems and be self supporting. Watch this
space for the next 50 years.
One thing we would ask, think hard before using man made materials unless
absolutely unavoidable. It might sound a bit hippy, but theres enough
concrete and plastic out there in the modern world, without having it all
around you in your private haven.