I'd assume that scrying requires a link, just like all other other thaumaturgy at a distance. Of course, you could veil yourself into the wardens office, take a piece of it away with you, and then scry on it... But, of course, the stuff you are probably interested in catching the warden doing will occur at 'random' times, and you are unlikely to be able to keep scrying going on him all the time...
So you are better off hiring hard to notice spies, The wee free folk appear to be both cheap and hard to notice, but then, they don't really seem to have the memory of social awareness to be really good at the job.
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Locations spells. Binder shaving his head in Turn Coat implies that the location spell effectively finds the hair rather than the person complete. Since Binder seems to think that this will prevent the hair based location spell from finding him.
Of course, having this sort of detail suddenly come up works fine in a book, but much less well in a game. Then it just soulds like the GM being a dick.
Have there been any general discussions of how thaumaturgy links work: how long they last, whether they can be deliberately broken, etc?
Questions to ask:
How 'macro' does the link need to be? For example, can I do the CSI trick of giving you a glass of water, and then pulling the discarded cells on the rim of the glass off? Are the shed cells any less viable that a bigger piece of you?
Do the ritual links link back to the whole 'metaphysical you', or only the part of you that is similar? (Turn Coat implies that it's only the part that is similar.) This would imply a world where (paranoid, i.e. long lived) wizards carefully removed all their hair, and, possibly, wore wigs. Which of course, they change out with great frequency, lest their wigs be made to explode...