scrublover

you don't need to cut it flat, though that makes it easier. if you don't, you actually have pretty good traction with the bark. until it falls of, which it will, eventually. then just cut some cross hatching into the top.

dirt or wood or built up rocks for your on. or don't built it so high to start with, so that you can get your wheels up there without needing a ramp. some of the trickiest skinnies i've ridden have been very low to the ground. width and curviness can make things pretty damn challenging to stay on even without having it high up.

exit? same thing, unless you want to always exit by wheelie dropping off the end or sides.

IMO, features like these are far better built into the flow of a trail rather than just "there" on their own. build into corners, front wheel only moves, uphill onto rocks that you then can drop or jump off, or have another skinny off the backside = challenge being you have to get angled right when on the rock to hit the new one. teetered versions. all sorts of stuff you can do.