[dawntwister]

I have seen a few like that before the plants are in. They start with the rocks, then the substrate, and then the plants. Plants tend to cover the rocks as they grow. Google rocks or slopes in the journal area and you should find some.

You could try make some terraces.
http://www.aquabotanic.com/dutchsecrets.htm

 

[dawntwister]

Here is a picture of slope started?

 

[dawntwister]

In this picture I have 2 terraces. Metal sheets are behind the rocks.

 

[dawntwister]

If it were me I would attempt to manufacture some type of plastic mold. or styrofoam carved to fit and then coated with something. I have seen it done on APC before, but not huge hills.

Sounds like what I have seen to make walls. "Great Stuff" foam is used.