Geyser spam from enemy hero - Any way to prevent it?

[Akimbo]

It's somewhat annoying, since if you're going for no losses you basically can't have any undead or demons in your army if the hero spams this spell every turn. I know sometimes doing something different will cause them to cast a different spell, but that's rarely the case. Is there a guarenteed way to avoid them casting this every turn?

Edit: I got past the battle that was annoying me, it actually went exactly the same except I attacked with one unit from a different angle, which seemed to make the Orc hero cast Bless (mass) instead of Geyser. Still, my question remains, how do you deal with Geyser in no loss games? Does it really boil down to having to use the same old boring Paladin based army?