That's an interesting link, nimbusllama, but I would be concerned that they're not being particularly scientific in their approach. For example, they describe a threefold approach of garlic, DE and resting pasture. However, even if the results are good, there's no way of knowing which of the three factors is causing those good results.
Likewise, to just have low FECs is not enough proof in and of itself - you'd need to show a reduction in FECs before and after dosing.
So, I don't want to be down on what they said if whatever they're doing seems to be working for them. However, for me it falls short of scientific proof.
Equally...
After dosing them with garlic, I lock the sheep in a dry paddock for a day or two, so they can pass any worms and/or eggs they might have in their systems. They then go out to graze in a fresh, rested paddock.
Wouldn't this accelerate the build-up of garlic resistant worms?