A variation of the infamous "cleveland steamer
" where you pull the girl's panties up over the poop after shitting on her chest.
A proper "tarp on a woodpile" is executed when you stretch the panties up over the poop while she is still wearing them (note that "granny panties" work best, thongs are quite challenging).
It is also acceptable (but not as desirable) if her panties have already been tossed aside to simply place them on top of the poo.
Tom, having grown tired of giving Viv nightly cleveland steamers
, decided to make good use of her laundry-day granny panties and give her a "Tarp on a Woodpile."
As a souvenir of the momentous occasion and Tom's inventive sexual aptitude, Viv had the granny panties framed and displayed in the living room for all to see. (She bought new ones for laundry day)