Strong turtles, securing rocks

[tinycat]

I plan to build a short stream and was wondering if there is a way to secure rocks to a liner so my turtles can't rearrange things. Or if securing is not feasible, how should the stream bed be shaped to avoid moving rocks? A shallow stream, most rocks are about 8" diameter, some twice that size, and lots of smaller rocks. The stream will be a meander with an elevation drop of about 24" over 10 feet. The stream will empty into a small pond, and will be fed at the top by a "waterfall" coming out of a skippy type filter. Turtles like to climb and grab onto rocks, and they are strong. 10" sliders. Currently, there is a big pile of dirt sitting next to and a bit above the pond, waiting for me to shape it.