I think Cave is a good spot, but the Nachal room is very small, they are wizards, soo, they can clean the whole room in 2/3 skills...
I'd say try Roc mount, in a wide area, but try going for the Eagles, and not Feather. Because Feather areas are very small. Black eagles area are more wide, and you can clean a lot of them in a single shot
Hope I helped...