I did the stacked rocks thing... I only had to cover 2 1/2 concrete
blocks and not very wide.. about 20 inches drop on the largest fall.
I built from the bottom up, in a U shape to minimize the splash.
Then, I backfilled the liner with dirt to add stability to the stacked
rocks and encourage the water come over them instead of behind them.
In addition, I cut a small piece of liner that is weighted down with
river rock and overlaps the top rock on the waterfall from the stream
above to get the water over the falls.

I am currently "attempting" to make an artifical rock out of
styrofoam, chicken wire and concrete. My test boulder has a complete
scratch coat on it and I have textured 2 sides to completion. It is
going pretty well so far and is a lot less expensive that rock. I
will see how the painting process goes this weekend and then I will
post pictures. If I like the results I will move on to a larger
project and create a larger waterfall using the same process.

btw, you can see my stacked rocks at the following URL under pond
construction.

http://members.cox.net/bokowski