It is a bit difficult to keep VM (vegetable matter--the stuff you don't want) out of fleeces, but one thing that helps is not to feed your sheep so that hay and chaff can fall out onto them. If they eat over each other they can get lots of stuff in their wool. Are they on pasture? Usually they stay pretty clean if they are only grazing and not being fed hay. How many sheep do you have and what breed? I have a flock of about 60 Shetland sheep and they don't have leg wool so I don't have to deal with that, but I imagine that leg wool is like belly wool and not too useful anyway. Jackets do keep wool clean and also from bleaching from the sun, but sometimes you need to have several sizes to accomodate size changes as wool grows so that it doesn't felt from being compressed. Do you have plans for this wool? If not, as someone already said, the bad stuff will be gone when you shear them. Hope this helps.