But with the british weather, it soon fills up!

 digging in is better, but I built my set above ground and they recover after a rain so much sooner. Since I cover them, they're rideable within 24 hours after a rain. You got that hillside to take dirt from right there.

 But if we dig into the hill side then its visible for the path/road .... Which mean it will last about 2days max before getting flattened :L but if we use dirt from the ground its hidden we can hide stuff in the holes and there below the water table so fill with water for drinking (when boiled) and for hardening the tracks/jumps