@Haru
Have you read Core? I had heard from somewhere, probably one of the Core re-write threads, that Aspects are/can be utilized more heavily in areas such as these. Also too I believe they added a mechanic for more flexible use of Aspects...something about Conditions or some such? Care to weigh in?
That's done by what is called "active opposition". It is sort of like a ramped up defense roll. You can do "Create Advantage" actions in Core, sort of what is now called a maneuver. You either create an aspect by that or get a free invoke on an existing aspect.
Now let's say you run away from someone and in the process you create the aspect "blocked door". You choose to make that an obstacle that your pursuer has to overcome by the means of an overcome action. The GM decides on the difficulty of that overcome roll. That's passive opposition. As long as your pursuer does not beat the obstacle with a reasonable skill (might to push open the door, for example), he can not follow you.
Now the same situation, but you pass one of your allies who is laying down cover fire by creating an advantage by the same name. The aspect now justifies him to roll active opposition each time someone tries to overcome the aspect with an overcome action. Instead of a fixed difficulty, the character can roll his shooting skill to see if he can keep the pursuers away. Since it is a roll, he is also allowed to invoke aspects on it to increase it.
Now you can do something similar for a magic shield. You use your magic skill to create the advantage "magic shield", or you decide beforehand, that your high concept of "wizard private eye" is enough of a justification, and then you can use your magic skill to defend against physical attacks. I like the first option better, because it coincides with Harry's "I readied my shield bracelet" mantra at the beginning of so many conflicts.
The justifying advantage can be overcome itself. Like Mavra did with the flamethrowers, for example. And once the aspect is gone, you can no longer use it to justify your active opposition, unless you can reestablish it again.
One of the authors did a pretty long piece on that, if you are interested:
http://www.faterpg.com/2013/richards-guide-to-blocks-and-obstacles-in-fate-core/#more-137