I can verify that he said something very similar to that (can't remember the exact words but "protective shield" was in there) on the air, either in his weekly radio speech or in a televised speech. I heard it with my own ears. That was earlier in the day before Charles Bishop flew his Cessna into that building in downtown Tampa and caused harm to no one but himself.
Another freeper on one of the threads that evening remarked "And Bush asked us to pray for the country's protection today. Think I'll try praying, it seems to work."