I'm not so sure a landlord would be very excited to know this had been built in the back of his rental property but over at Dwell's Blog Show Your Space Tim explained it this way: I built a wooden skateboard bowl in the backyard of a house I rented and used mostly scrap wood to do it.

The bowl blends into the yard so well that my landlord had been over many times never even knew it was there. We had ramps going up trees and trees built into the decks. I had people coming over to skate from all over the world. you can see more images of Tim's bowl here.

Back in the mid 80's [dating ourselves here] good friends of ours built half-pipes in their back yards [with their parent's permission] and when an insurance agent came by to do an standard assement on something unrelated, he said they had to remove the half-pipe or the home owner's insurance would be cancelled [no word on if an extra rider policy was available] sadly, it was dismantled yet despite the tear down, both boys went on to be [short lived] pro's.