I had (I thought) pretty good luck with a combination of terrains and individual coins, although it was a painful process to create and arrange the individual coins. The terrains went in the background where they are hard to see to avoid having to create a billion coins, and were created by making a smooth terrain of the appropriate shape, then setting the paintbrush to be very hard and coin sized. Set the paintbrush level to dark, and click a bunch of dots all over the terrain to create the bottom level of coins. Make the level slightly lighter, and click again, but closer to the center. Repeat, adding less and less to each layer. You will end up with something like the attached pic, which is one of my coin piles. I'm sure there's a faster way to do it, but this worked for me.