If I had wanted to achieve a "Zen" fountain look, I would have created a neat, solid circle of the polished river rock around my fountain. To do so, however, would have required far more polished river rock than what I had. Instead, I used other rock (mainly flat rocks) that I had at my disposal to fill up most of the space around my fountain -- and to cover my grate, so that the polished river rock wouldn't fall through (see Step 9).
The river rock serves as an accent at the base of my stone fountain, but it would also serve a practical purpose if I were using a more powerful pump: having smaller, rounded rocks in that spot would mean less splashing and, consequently, less water loss. The cascading water would gently strike the polished river rock and ease back down into the reservoir of the pond liner underneath the fountain.
The following link will take you back to Step 1, where you can review my picture of the completed stone fountain.