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That DM does seem a little unreasonable, but you're right, his methods do work. A more reasonable approach would be to simply have monsters and NPCs with True Seeing happen across the portal.
As for the extradimensional spaces argument, I know its an old one, but I don't think it's...
5 out of 5 rating for Pathfinder Roleplaying Game: GameMastery Guide
This is one of the few books that does a great job of introducing refereeing and honing existing skills for the experienced referee. Useful far beyond the scope of simply Pathfinder.
I was always partial to the oratorical bard. They're still using an auditory performance, but it made a lot of sense in a historical/dramatic sort of way. A general giving an inspiring speech makes a whole lot more sense than a musician running around the battlefield with bagpipes.