Australian/NZ informal unreasonable or unacceptable.
side of the fence
used to refer to either of the opposing positions or interests involved in a particular situation:whatever side of the fence you are on, the debate on conventional versus organic farming is not going to disappear
sit on the fence
avoid making a decision or choice.
Middle English (in the sense 'defending, defence'): shortening of defence. Compare with fencible and fend