Can you Unenchant something?

Open up your enchanting screen by right-clicking the enchantment table. The enchanting screen will show, with a place where you can place items, and 3 buttons. Select the tool or armor or other item (like a book) to be enchanted. Hoes, shears, and horse armor cannot be enchanted on a table.

How long do enchantments last in magic?

An enchantment is a permanent. See rule 303, “Enchantments.” See also Aura. 303.1. A player who has priority may cast an enchantment card from their hand during a main phase of their turn when the stack is empty.

Can you double enchant a creature in Magic?

Yes you can. The only limit on enchantments is the same limit that all permanents have: the Legendary rule. You can only have 1 permanent in play of a given name if they are legendary. However, even if you enchant a creature with the same enchantment, subsequent enchantments might not do anything.

Is an aura a permanent?

Auras are indeed permanent cards. The only card types that do not count as permanent cards are instant and sorcery.