I would recommend that when Arab is on and posts, ban the /24 he/she/it is on, then when it switches to a new /24, release the ban on the previous /24, and institute it on the new /24.

Time intensive, yes. Work intensive, no. But, if he/she/it is responsible, it would cut the shilling down tremendously, with him only being able to post once before being banned. It would be a minor inconvenience to real Anons.