I like the ideas of brass or leather rings lower down on the tusks which are connected to the walls. Personally instead of the materials listed above I would get a set of plainish Ebony rings made with a silver loop on one side. Then connect a straight piece of Ebony to the loop on the ring on one side and into the wall (with a matching loop or something) on the other.

I think Ebony contrasts very nicely with Ivory and has the African feel to it. Maybe a nice Ebony base as well.

Any word on progress? You are just down the road from me a bit.