After getting quotes on a pondless waterfall installation, my wife and i decided to install one ourselves. The problem now is that I've got leaks springing up along my streambeds. It was reccomended that I use Gret Stuff! foam sealant between the rocks. It is now looking like I have more foam than rocks. Any advice on products to use to seal between the rocks?

Great Stuff is not waterproof! It will divert water but will not form a seal. Your problem is with your liner in the stream bed. If you were careless or too hasty with the liner joins ( not enough sealer, or not enough overlap or not enough cure time), your joins will leak like seives. You may not have allowed enough extra width at stream's edge to accomodate splash and turbulence, or your streams may simply be too shallow for your flows. Look at the back of your falls reservoir. If your flows are too high for your falls outlet, you could be losing water from the back of the falls.

Did you carefully place the rock into your stream bed, or did you just drop it in? Depending on what kind of liner the kit supplied, it is entirely possible that a jagged edge of a rock has perforated your liner. The lightweight liners supplied in the kits are often undersized, very fragile, and prone to these types of leaks. 44 mil EPDM butyl rubber remains the best and most cost-effective material available.

Rip out the Great Stuff, then get the rocks out. Look for the damp spots under the liner. The leak will be obvious.

(Answer courtesy Bob Passovoy)