When I learned how to program computers, I was told to "Code as if you are going to throw it all away, because you probably will anyway." (It's a famous quote, the origin of it escapes me). I take the same approach to designing arcs. My outlines are very minimal, rough, and I always expect many changes and high entropy (especially with the involvement of other characters being as unpredictable as it is in an RP). Normally I just put together a list of dot points with sublists of more detailed dot points when I get close to them in the canon IC.

The 'many changes' thing is no joke. It makes conventional outlining wholly inappropriate. Toun's arc has twisted so many times that I get nauseous trying to go back and reconcile his character development. On the other hand, I have saved a lot of wasted effort by keeping the forward planning very terse.

EDIT: Wait, Belru has a holy site?