You surround yourself and your allies with a ward of thunder, which batters your enemies. One of your allies carries your mark of protection, so if your foes attack that ally, the ward erupts in thunder again.

Daily   ✦     Divine, Implement, Thunder, Zone
Standard Action      Area burst 2 within 10 squares

Target: Each enemy in the burst

Attack: Wisdom vs. Fortitude

Hit: 5d6 + Wisdom modifier thunder damage.

Effect: The burst creates a zone of warding thunder that lasts until the end of your next turn. Choose an ally when the zone is created. If any enemy attacks that ally, you can make the following attack against each enemy within the zone as a free action:
    Attack: Wisdom vs. Fortitude
    Hit: 5d6 + Wisdom modifier thunder damage.

Sustain Minor: The zone persists.

Revision (10/13/2009)
On the Effect line, replace the last sentence with the following:

If any enemy attacks that ally, you can make the following attack against each enemy within the zone as a free action:
    Attack: Wisdom vs. Fortitude
    Hit: 5d6 + Wisdom modifier thunder damage.

Published in Player's Handbook 2, page(s) 117.