usually a parenthesis with corresponding character is used to be explicit or to avoid confusion but its strictly for chinese loan words like:

ex) 시간 (時間)

compared to furigana (note that its not even possible to display the phonetic hiragana): 第二巻

younger generation are no longer learning Chinese so more English/European loan words are directly used which ironically fixes the issue.

it is impossible to converse in Korean without using English/European loan words

ex) 아이러니 (irony)

This allows new ideas/concepts to quickly disseminate in the collective Korean psyche. Constantly new words are being invented, slangs used by primary/middle school are unknowable.

Abbreviation/concat combos to create totally new words:

ex) 씹상타치 (way **ing above average) also written as ㅆㅅㅌㅊ (wfaa) literally means