[Alneyan]

Earth Attack and Mind Hunt also don't work against units busy hiding. Leprosy, Fires from Afar, Murdering Winter and Flames from the Skies should work fine, though, but that will only be a threat for them if:

A) They are in the same province as a big army of yours.
B) The enemy is using Astral Window to count how many units you have exactly and notices an increase in a province where there are Devils.

Even in these situations, your scouts still have a pretty good chance of making it through, and keeping them somewhere quiet should greatly increase their life expectancy. Alternatively, just put them somewhere under the sea, where they will be immune to everything except Leprosy (I think).