haha this post has me cracking up!!
anyway, I used to have that problem with my boy so we keep his bottom clean-clipped so there's no hair to encourage dingleberries lol
on the other hand, this happens with my cats, except they don't drop off anywhere. it just stays stuck to their little behinds. baby wipes are perfect for the job... it's not the most fun thing in the world, but it keeps them clean and comfy.
I'd recommend luring them with treats one-by-one or catching them before they run back into the house (crack the door a bit and head them off at the pass) and be ready with a baby wipe!