like a cow on a flat rock

The rain alone could have been tolerated. The skies opened torrentially every morning, afternoon, evening and night. “Like a cow on a flat rock,” old Navy hands said. In between the sun shone and generated steam wherever water lay. Men's shirts were never dry save for one fleeting instant when the sun had finished evaporating rain water and sweat had not yet started to pour.

1983, James A. Michener, Tales of the South Pacific, page 338

"Get in here out of that." "It's too late now," Winer said. "I don't see how I can get any wetter." […] "It's fell a flood, ain't it?" "Like a cow on a flat rock," Oliver agreed.

1999, William Gay, The Long Home, page 15

I had to pee like a cow on a flat rock, but I wasn't getting down [off the top of the refrigerator] until she either put the demon [dog] outside or shot him with a tranquilizer dart. Even then, he'd have to twitch for five minutes before the coast could be considered clear.

2014, Linda Lael Miller, Deadly Gamble, page 145

"At six [in the] morning, he's pissing like a cow on a flat rock, and at seven he's shitting like a wild elephant." "So what is the problem?" "He doesn't wake until eight!" "Ah!"

2019, Ian Wood, Merde on the Orient Express

The other was holding her pants out of the way, because she was pissing like a cow on a flat rock, and the flat rock was Buck's WELCOME mat.

2010, Ben E. Terry, Dancing with the Devil, page 9