i came up on a idea of a obstacle that you'd have to bunnyhop thru.
basically some kind of a staircase made of planks and steel pillars that you couldn't just ride up but youd have to bunnyhop a.k.a. jump only with back wheel up it....

dunno if it's possible to do so that you couldn't just ride it up but it would be fun (and hard) in my opinion =)