Here's a tricky one that I can't quite figure out the correct punctuation for. How do you write the possessive of a noun which is already possessive? The example which spawned this question:
How would you describe something belonging to St. John's, where St. John's is any of the colleges, towns or hospitals which bear this name, including the apostrophe, and not the saint?
@waiwai933: This is what I've always done, I just wondered if there was any clever punctuation you could use to avoid this kind of rephrasing. I'm guessing from your immediate reply that the answer is probably no, but I'll see if anyone else comes up with something interesting.