Suppose I control Umbra Mystic and a land that's also an Aura.
(Note that I could find no combination of cards that could actually create an Aura land, so this question may just be pie in the sky. I did find a convoluted way to create an Equipment land but that's probably not relevant.)
An opponent casts a spell to destroy the creature the Aura land is attached to. With totem armor, the Aura land is to be destroyed instead. Can I tap another land enchanted with Equinox to counter that spell?
My instinct is to say no, because the replacement effect adds a layer of indirection to the spell, such that the spell is not what destroys the land.