Random idea that popped into my head:
Illusion: Allow the character to hide all spell visual effects. (Stoneskin, Shadowshield Premo etc.)
Divination: Allow the character to discern all spells another pc is wearing, either through examine or command.
Abjuration: Allow a character to force hidden spell visuals visible.
Epic Spell Focus: Illusion, Divination, Abjuration
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