why do you poo pick? Its the fastest way to rape your soil? You will end up with lower quality grass which will impact the growth and health of your sheep. Its one of the reasons horse pasture gets sick so fast!
The single best thing you can do to prevent it is rotate pasture, keep worms down and ANY animals that scour, dont breed from and remove them from your flock.
I have perhaps 1 in 150 now each year that scour and get shitty back ends, all from culling. Its a death sentence, concurrently removing them has also meant I have bred for worm resistance.
I do not click or crovect mine - I shear them late (Early to mid June) So the fleece is at its shortest during peak fly season, which is good protection, look over them daily, and as they are moved every 5-7 days they are handled.
Any that get struck are treated, they are also given a square notch to the ear and a sent for killing when ready - I've found by doing that I've reduced the strike rate on an UNTREATED flock, from 1 in 10 in 2011 to 1 in 120 so far this year. Interestingly I now have sheep with less wool round their bums and tails, and most of them have courser wool than usual for mules and lowland crosses.