We went above ground for the reasons you stated. You can see it on
the pond link with our Google profile. We used treated 2 x 8 lumber
for the sides and allowed the EDPM to be the bottom. Easy to build.
The bottom drains (2") make it a breeze to clean the ponds. A berm is
a small hill. We had the dirt dumped, shaped it with a tractor and
box blade and dug the holes for the berms and waterfalls. Doesn't
look as much fake as it does add a backdrop tot he pond...we think.

Jim