There's a suggestion floating around on tech blogs for setting 'unguessable passcodes' in iOS. The idea is to use alternate accented characters, which are hidden but easily accessible by holding down letters on the virtual keyboard. The thinking is these accented characters could be especially effective at thwarting guesses, as English speakers might not even realize that there are accents beneath the keys...
Accented characters make iOS passwords stronger, not enough to keep your data secure