You may target any permanent with the triggered ability, not just one controlled by the defending player. If no other player controls a permanent, you must target one of your own.
01-01-2011
wotc
The second ability triggers and resolves during the declare attackers step. The target permanent will be destroyed before blockers are declared.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.