Pond Boss Forums INTRO Questions & Observations Best way to block outflow pipe from pond?

With no input as to whether or not it would be a good idea, you could stack Quikrete bags instead of sandbags or pouring concrete. They will conform to the curves (like sandbags) but will harden in place and (if you use enough depth) lock together fairly well to resist water pushing them.

Warning: Handling enough 60 pound Quikrete bags may lead to your introduction to the Double Hernia Robotic Surgeon. For me, 5 pallets of Quikrete were enough.