The Japanese word baba is similar to poop in the sense that it's also infant-speak and generally means poop. Neko means cat. Nekobaba means covering up misdeeds by feigning ignorance, especially when keeping something that is not yours. This idiom has atleast two theories of origin. One is that it is based on the observation that cats cover up evidence of defecating. Another theory is that there was a cat-loving old woman during the Edo era who was always reluctant in returning borrowed items. Baba also means old woman. Calling someone as old is probably the most offensive thing you can say to a Japanese woman, so be sure not to call them babaa. I don't think the idiom is suggesting one to bury money like cats bury poop, just as the idiom the early bird gets the worm isn't a suggestion for eating worms in the morning.