Any missing ideas?

I want to create a status effect on units that makes them miss on attacks, but here's the catch-- it can't be dispelled, and the duration will differ. The only way I can think of to accomplish that is to give whatever they attack evasion for a quick period of time, and that's a bit iffy.

Use curse, set a custom level of miss chance, and set it to have a really long duration, which if it does end, is restarted by a new casting of the spell from an invisible neutral hostile unit which is destryoed after it casts curse.