even if you could make the flip the unicycle would just roll out from under you when you tried to land.
no way dude ... if you landed it and it did roll out from under you ... then you either over or underotated ... im going to try one off about a 2 ft ledge into about a foot of water next weekend so we'll see how it goes, but even if i do land it in the water ... it wont be all that amazing, but it is definitely possible
