[@Dezuel]

The barrier is visible. The very clip you mention uses a barrier equal to the one Nanoha cast, in most aspect. If he's aware of Magic, he should be able to spot it from kilometers away. I mean, it's big enough to engulf a whole city. See:

[center][youtube]https://www.youtube.com/watch?v=iT2HzCg36x0[/youtube][/center]