Compact the Rock
Use a plate compactor (rent for roughly $60 a day) to tamp down the rock. Remember, make sure to pick a rock – like decomposed granite – that compacts well but doesn't pack too tightly for water to get through. Run the compactor over the surface several times, checking for humps and slope.
Wear safety glasses and ear protection when working with the plate compactor. These powerful machines can be difficult to control; if you're not confident you can control the compactor safely, get help or call in a pro.