You should probably look at invasive species to get the hill under control, but saying you must be able to protect species from growing out of bounds. Invasive will grow faster which is what I assume you want. Like periwinkle.

Here is a link that might be useful: Propagating Perennials

Thanks. Lots of reading! Terraces should be completed in a couple weeks then I will get started.

I am using creeping phlox, with campanula and creeping thyme on the steep slope.
I don't like vines that are invasive, such a chore to rid when time to go. Bad enough i am tearing out old blue rug juniper, tough woody stems.
Also, you might want to look into Ribbon grass,I have seem banks with that and they look awesome, but be careful with that one, it will take over and tough to remove.
If course there is the standard for slopes, daylilies.

I found this info very interesting -
(link below)

When searching, you may want to look for aggressive plants. My preference is for natives. If you do choose an "alien" please make sure it doesn't fall in the invasive category.
invasive plants aren't eco-friendly. The problems that these nasties cause will reach much farther than your land.

Invasive Species:

"An alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health."

good luck

Here is a link that might be useful: native plant root systems

If you have full sun and the right zone for it, try creeping rosemary (sometimes call cascading or groundcover).

If you want a groundcover that is very aggressive, St. John's Wort, hypericum calycinum will do it.

Another groundcover shrubby plant is cotoneaster. Some states consider it invasive (birds eat the berries and pass them along, so to speak).

Creeping thyme is another good one for full sun.

Creeping phlox (phlox subulata) is also great and colorful.

Clematis vines, though not evergreen, provide nice blooms.

If jasmine works in your area, that's another possibility. The foliage is evergreen here in NC.

You can tuck sedums into cracks and crevices of walls with little pockets of dirt.

Again, zone permitting, delosperma cooperii (ice plant) is another full sun possiblility. Evergreen here, loaded with sparkling flowers all summer (they close at night).

Here is a link that might be useful: my gardening blog