The only horses I've seen with thrush- hooves don't get picked daily, or are stalled. When you force a horse to stand in manure and urine you're exposing them to alot of dangerous bacteria. Unless you stand there for 8 hours and pick up poops and urine right as they come out, you going to make them stand in it.
Now I watch every horse I shoe like a hawk and anything that resembles WLD I treat immediately.
Copper sulfate solution is on the shelf in a squeeze bottle and I use it daily on the horses feet in any crack or crevice I can find.