Instead of waiting for "Fenrir" (which your opponent can nullify by getting rid of either monster or by just not entering their Battle Phase), activate a face-down "Final Attack Orders" or "Battle Mania" to inflict the 3000 damage.
After your opponent changes this card to Attack Position, you can use cards like "Creature Swap" to take it back. Or, if you run "The Nordic Lights", you can easily get rid of this card, should "The Nordic Lights" be destroyed.