If you use the ADa aqua soil, it's a clay, so you can mold it somewhat gently and it'll stay put. That makes it very cool to me, Flourite and most other sands etc fall flat unless you keep on it and redo the gravel every month or two etc till things root in well.
Basically, THE ADA AS IS THE BEST PRODUCT AROUND FOR MAKING HILLS.
Regards,
Tom Barr