Yeah, you'd have to use stercorum if you wanted to be accurate. Not that anyone is going to notice either way you do it -- people usually believe what you tell 'em if they have no idea
Lovely use of the partitive genitive Looks good to me. Wondering about the original sentence too though...what meaning of show are you wanting? It could influence which verb works best, there may be a better alternative to monstro.
genitive? mihi, if thats what u mean , is dative monstri is imperative mood stercorum is accusitive. w/e
Jesus, my Latin is so rusty after two years of neglect I was actually looking at stercorum, but of course it's accusative. Partitive genitive in that case would be "nullum stercoris" or something, wouldn't it... Just ignore me, I'm a uni dropout