A lot of people use sand and sift through it, now and then.
You'll need a front end loader or something similar (like a bobcat), to pick up the sand/lead and dump it into a sifter. It's kind of like a mining operation.
If you want to go smaller, you can make a wood box to whatever dimensions you so desire (as long as it is about 24" deep, from the target face) and fill it with
rubber landscape mulch. You still have to sort through all the mulch for your lead - but it will be in there - and not dirty.