How do I make a fake rock finish for a water feature?
There are several types of silicone molds that can be filled with regular concrete. There is a limited selection at the box stores, but you can find lots of different designs online. These are nice because you can use cheap bagged concrete mix, add colored dye if you want or even put in real stones and embed with the concrete.  Most of these molds are fairly small, 3 ft by 3ft and make 2 to 4 stones each.