My memory may be failing, last time (15 years ish? ) I looked at living / staying in Korea most places asked for a full years rent up front, then additional rent each month. You are supposed to get it back at the end of the lease. It would be trivial for a land lord to abuse a foreigner in this circumstance on the VISA, its not like you can stay around after the end of your lease to take them to court to recoup your money.

I'd be very careful about this.