I may be wrong with some parts but it was an interesting translation activity for me. If I am wrong - please correct me.

동해(dong-hae/east) 물과(mul-gwa/sea and) 백두산이(baek-doo-sa-nee/mt. baek) 마르고(ma-reu-go/ drys up and) 닳도록(dal-do-rok/until worn away),

Until the East sea dries up and Mt. Baek is worn away,

하느님이(ha-neu-nee-mee/god) 보우하사(bo-oo-ha-sa/protect) 우리나라(oo-ree-na-ra/our country) 만세(man-se/eternity),

God please protect our country forever,

남산(nam-san/Mt. Nam) 위에(wie-ae/on top of) 저(jeo/the) 소나무(so-na-moo/pine tree) 철갑을(cheol-ga-beul/iron armour) 두른(doo-reun/enclosed in) 듯(deut/like) 바람서리(ba-ram-seo-ree/frosty wind) 불변함은(bool-byeon-ha-meun/unchanging) 우리(oo-ree/our) 기상일세(gee-sang-il-se/spirit of a generation),

The pine tree on top of Mt.Nam is enclosed in iron armour from frosty winds like the unchanging spirit of our generation,

가을(ga-eul/autumn) 하늘(ha-neul/sky) 공활한데*(gong-hwal-han-de/big and wide but feels empty*) 높고(nop-go/high) 구름(gu-reum/clouds) 없이(eop-she/not there),

The autumn sky is big and wide but feels empty and high with no clouds in the sky, ( * I couldn't find out what 공활 meant - all I got was republican so I had to ask my Korean friend for some help....^^)

밝은(bal-geun/bright) 달은(da-reun/moon) 우리(oo-ree/our) 가슴(ga-seum/heart) 일편단심일세(il-pyeon-dan-si-mil-se/sincere generation),

The bright moon is the heart of our sincere generation,