I doubt that an iron cage would prove much of an obstacle for someone who can do this. As an aside though, you probably wouldn’t have nearly as many problems with zombies if you’d just leave the dead alone. Stop bringing them back from the grave! Do you think maybe this kind of thing could maybe, possibly, perhaps get out of control? Maybe it could backfire at some point. Someone else takes control of your zombies; the zombies start doing stuff you don’t want them to, eating things you didn’t want them to, because they don’t care whose brains they’re going after. Maybe someone will come along when you’re dead and bring you back, and how will you like it then? But right. Of course that won’t happen to you, because you’re a god-dragon/demonlord/necromancer-who-knows-the-secret-to-eternal-youth/mad-scientist-who-doesn’t-care/someone-who’s-already-dead.
Innistrad is stupid.
10,000 Reasons Why the MTG Multiverse is a Terrible Place to Live 