Question: thoughts on mammoths?

[Dogboy]

My Helheim (EA, CBM 1.95) horsemen and Valkyries are getting crushed by Caelum mammoths. Are prison of fire and false fetters equally effective at stopping their trampling feet? Also, considering clockwork horrors against them, on the idea that swarms of the little devils could kill the elephants before they start stamping me. But, they're small and have low HP, so I'm guessing they'd be flattened like tin cans if I don't time it just right....