baranka, buraku, buriku

I'm having trouble keeping these three words correct in my memory: baranka, buraku, buriku.

Sometimes I can remember buriku (donkey) by thinking of the Spanish word burro and then thinking of Riku, which is one of my nicknames.

Need to find a memory-hook for baranka (rock) and buraku (hole), something for the memory to hang its hat on.

Buraku probably comes from Portuguese buraco, but what’s the source of baranka?