Exactly like Reinha said. Reapply it for dps right when they lose it during the fight, reapply it for the tank just when the last monster dies (should be timed perfectly with regen running out too). If you did not have the time to do that because the pull was especially hard or you were very busy dpsing, Swiftcast/Lightspeed and you can apply it while the group is moving towards the next pull.