A phrase your grandparent might use to describe being busy with a futile, impossible, or endless task.
Cats like to cover their feces, but if they've done their business on a frozen pond, no matter how long they try to dig up something to cover it with, their paws
will always slide on the ice. The
joke is the mental image of a cat making the digging motion on ice for a long
time.
I don't
know why I keep
weeding that garden. I've been busier than a cat trying to bury a
turd on a frozen pond, but I tell you what, there's gonna be just as many dandelions tomorrow.