Hey~ I'm preparing to DM a one-off (or maybe two-off) session for three people in Pathfinder. The premise is that they're in a large city, the capital of GenericFantasySettingKingdom, and that a new king is going to be coronated in one month, and the PCs, who will all be rogues or bards, want to steal the crown jewels before they're locked up again afterwards. They'll be 10th level, but the NPCs that will attend the event will mostly be higher than that (the king will be a 20th level barbarian. Yeah, he's pretty much Conan).

I'd like your advice on what kind of security measures that I can put in place for the PCs to overcome, Ocean's Eleven-style. So far I've cone up with:

-the jewels will be a sceptre, kept in an adamantine vault, a ring, which the king-to-be never takes off except to sleep and bathe, and a crown, which will be forged from the smelted-down crown of the previous king a week before the coronation.

-There will be a semi-public coronation, which the city's wealthy and elite will attend, and a private coronation, which the king's personal friends, including his old adventuring buddies, and some honoured guests will attend. The king will not be surrounded by royal guards during the private coronation.

-No (or very few) anti-magic fields, since the king's personal guests will include various magical creatures, including a Wyrm Gold Dragon. Instead, a team of wizards will monitor the castle and grounds, alert for suspicious spell casting.

But I know my creativity could never rival Reddit's, so what do you guys think would be fun to include?

Edit: Spelling