Composition of an Elite City Guard Unit?
Since we can't expect the city guard to be able to outfit their men, even their elite guards, with enough magic items to match those used by an adventuring party, they'll have to find other ways to level the playing field. Some examples might be equipping the group with one or more Rods of Negation. Or having a Wizard or Cleric who is high enough level to cast Antimagic Field.They will also need to have a way of seeing through the various disguises, illusions, and transmutations. Goggles of True Seeing might be a good choice.
Even if they aren't able to compete with the higher level magic users, summoning lots of smaller creatures and having them grapple the caster will help to prevent the magic users from walking all over the guards.
Most big cities tend to have Adventurer's Guilds where retired adventurers go to swap stories and write their memoirs. Perhaps when a powerful group of adventurers goes rampaging through the town, the retired ones strap on their armor, dust off their holy symbols, and grab their spellbooks in order to help get the newcomers under control.
There's also the really powerful people for the larger cities to fall back on: the Wiz20 who runs the Mage Academy, the Clr18 who heads the Temple of Bosk, and the Rog19 Guildmaster of the local thieves guild. I'm sure they wouldn't take it too kindly if a group of people comes in and decides to run amok through their city.
Utimately, I don't think it's possible for most cities to have a group of city guards who are able to handle a party of high level adventurers. The system kinda breaks down when the PCs get into the higher levels, but the average person is still just a Com1, and the average city guard is only a War1. They'll probably have to rely on outside help if the situation ever occurs (which it shouldn't very often...)
Sorta like the Gotham City police flashing the Bat Signal every time a supervillain gets out of control.
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