I think poop is a little too strong a word for THR. Perhaps you could drop the last "p" and refer to it as "poo"...
Isn't that better?
And to be a really efficient dog poo fly hunter, you must hit them just as they begin their final flare on landing.
Of course, like duck hunting, as you pop out of the blind (you ARE using a blind aren't you?), they begin to back pedal so your lead is somewhat of a challenge, depending on the wind, size and speed of said fly (big blue bottle flys vs. those pesky little black jobs) when using air guns. In any case, I prefer to place my blind upwind as opposed to downwind.
Now for the really big dangerous boys, horse flys, I prefer horse doo, not cow or dog poo as my bait of choice and here I think I'd suggest something with a bit more bite, as it were, than a simple airgun. But be warned, these critters are nasty and they can turn on you if you miss, so you'd better have a guide along as backup
I've got to try that coke/sugar water trick sometime... just seems so cruel as it doesn't really give them a sporting chance, though.
Adios