earth construction

I have a rammed earth wall being constructed outside as a retaining wall and inside as a pony wall. First project is coming along great but, wondering how to seal it using a natural eco-friendly material. Envision a live wall with moss or other green vegetation so, would hope the sealant would not preclude cultivating on the surface. Sealant should also have surface hardening efficacy as well as protecting against water erosion. So, specifics: natural, non-toxic, eco-friendly; hardener to create enduring resilience (e.g., heavy objects banging into wall yet integrity maintained); water/moisture seal/protectant; surface amenable to live plants (e.g, moss wall). Any ideas of products that would fulfill these criteria?

I've often considered plants in cob walls or methods of allowing vines and such to easily travel the wall both vertically and horizontally and through the wall as well.

Windows are easy to allow plants to pass from one side to the other. I think you can train vines with loops, pegs and grooves to move vines.

Now the hard part and your original question (sorry). Cob and natural building materials will break down if plants try to drive roots into their structure (shocking I know!) I think you could make a "clay pot" with cob in a wall and treat it in a few different ways to make it last. Make sure you leave 1 or multiple weap holes for water and soil residue, perhaps the design of the "pot" can be planned to take the run-off, like a beard or waterfall as it changes color.
1. lime/clay/sand: coating the interior of your "pot/vessel" and burnishing to to have a more glazed aspect. Lime may effect your plant in a negative way.
2. linseed oil: It's pretty cheap and really works well on cob and soil based surfaces, they need to be poressed (sp. I know it's spelled wrong but the spel chequr doesn't have a clue) and dry to absorb well and not subjected to heat, sun is fine.
3. burn it: Fire bakes clay, curing it and preserving it for.. well a long damn time. Remember when it burns and dries it will shrink. Cob roughly dries as one mass, if you put heat in one area expect cracking unless you add extra mass and moisture, maybe even filling in over time. Maybe daily as it dries.

Thanks for the reply Rick.

See Rammed Earth Pics: The surfaces have some fines(sand, iron oxides) that are not very abrasive & rub right off. I tried linseed oil (bottom of end, brown boiled) it darkens the wall quite a bit, and a water based acrylic concrete sealer not as dark but still unacceptable. Any ideas on a clear sealer that won't darken? The mix is soil, sand, limestone.

When I build a home I'd like to keep the interior wall permeable and breathable. This retaining wall I want to protect from erosion, the elements, so it can have a lower perm or barrier sealer.