Harry can bring up a shield almost instantly. He's also used his shield to project a kind of force field as a flat plane before; he could very quickly create a circle trap if he did it around a group of bad dudes from the Nevernever, for example.
well I was referring to a solid carry on the arm kinda shield. No comment on if Harry's crazy enough to make a magic circle out of pure magic. :x
Since he can do magic in his mind already, he has no need to cast a shield circle, I'd think.
