I went to a building supply store today and found some perfect base rock. It is Apache Pot rock. It is like lava rock but much more dense. It is still very porous though. The shapes are perfect, there are some flat, some square, for the base, and some pieces with natural little caves and tunnels in them. And the best part was the price, 45 cents a pound! Right now I have it curing in a trash can, I just want to monitor the water chemistry and make sure this rock doesn't change it somehow. Hopefully it will be fine. Its a lot cheaper than the $2 a pound marshall base rock I was gonna buy