Yea you can make a Skate Park or whatever you want out of dirt look at this picture i saw ages ago on NSMB and it doesn't look like they used carpet.
View attachment 111493
Thats pretty sweet, however, when the local council made our local skate park, thaks what it looked like before they concreted it,
Heres a sweet tip i picked up off a mate who builds Motocross tracks...,
Build your jumps,
while they are setting/ curing;
- Lay chicken wire over lip's and cover with a bit more dirt and cement powder.
- Compact with roller/ heavy blunt object
carpet rots and goes blahhhhh after awhile... chicken wire, even when in moist dirt won't rust and cause punctures.....
oh well,
hope i contributed constructively,
jb