I'd 'anchor' the bed with a few upright plants- Yucca are indestructable, and the roots go DEEP. and to really hold a bed together, you want a variety of root depths.

dwarf (low-grow) sumac is an option- I only just heard of the stuff this year, but if I had a barren hill, that's what I'd fill it in with, for the blazing fall foliage alone.

daylillies work, as would a ground cover rose.

there's also 'yellow archangel' as it's called in the hortiplex- it's aggressive, attractive, and cheap to propagate yourself- and semi-evergreen in my neck of the woods, taboot.