Translation:A mountain slope is not a good place for a farm.
“Oblikvejo” (oblikva = slanted) might be a possibility. But it does not seem to be widely used at all, and oblikva can refer to a deviation from the vertical as well as from the horizontal.
“Klinejo” is also somewhat ambiguous as *klini' does not only mean “to tilt” but also “to bend (sth) down,” “to bow (sth).”
So there seem to be good reasons for the root “dekliv-.”
Says who? I think that a mountain slope would be an excellent place for a farm.
@Raztastic, for a good explanation and history about "bieno", see this discussion from the Duolingo EO Facebook group: https://www.facebook.com/groups/duolingo.esperanto.learners/permalink/531338803694808/