I've buried wood logs and pallets under my jumps and berms. And, yes, you will "wear" your way down to the "stuff" underneath.....but, I think it's worth it. Because it saves a lot of finding all that extra dirt. Plus, when it starts to show thru.....that just means you need to do some maintanence. It's not that hard......just skim the surface of the areas around the jumps/berms(that where all the dirt went!) and put it back on top. I mean, if you're talking jumps 4' high.....wow.....you are looking to move a crap-load of dirt......and burying something will REALLY help eliminate moving so much dirt.

My backyard track took me several weeks to complete......would've taken much more longer if I didn't bury anything. That was a time saver!

Good luck and post pics!

Ob1n of RCU