in terms of sloping... you can use slate or other inert stone under the substrate to create a terrace... or plexiglass... the ADA group sells a stainless steel stepped terrace plate for use under gravel, and they put their heaters under it... which seems like a nightmare if the heater fails...
a few well placed stones at the base of the slope will also help a lot with erosion, by creating a partial wall here and there... and of course plants that root quickly will help maintain the slope as well, as long as you don't vac around them much or disturb them.
it's true though, gravity will try to level it all out over time. that's why it's important to build it up higher than you want in the long run. as long as things like rocks and roots keep the slope while everything gets established, it ought to maintain a lot of it's contour long enough to settle.
