I have a very good client that wants their trampoline buried in a pit, so that the jump surface is level with the surrounding lawn. The problems I see is drainage, a solid base for the frame, and want to use to keep the surrounding dirt from falling into the pit without creating a hazard. Any suggestions would be appreciated. The soil in the area has a high clay content, so the drainage system I picture is something like a French drain. My idea for the dirt from the pit would be to use it to raise the surrounding area, so that any rain will run away from the pit. So, the only water to deal with would be direct rainfall, which is about 50" a year (record for one day is about 8"). What I'm really concerned with is the safety issues. The family has three very active girls, with one a gymnast, and another a diver, this will get used alot. Thus, the need for a foundation and side walls built to last, while not creating any extra hazards.