Waterfall repair--Great Stuff?

We need to seal up some leaking in our watefall. The waterfall/pond is about
5 years old and is the victim of settling so we have cracks between rocks
and the
cement. The pond is not leaking fortunately. The pond water is currently low
due
to evaporation and not very much spring rain.
Anyway, I have heard some people mention using Great Stuff (never even heard
of it prior to reading posts in various places)
to deal with leaks.
Is it a temporary fix or does it do a pretty good job? What else could be
used
to deal with cracks and loose rocks? Any suggestions of a better way to
accomplish a leak free waterfall or how
to best use Great Stuff would be appreciated. Thanks!