[doofus47]

Ok, I'll bite. I shoot often enough on public land to have made some personal rules.
1. Pack it in/Pack it out. I bring my own targets. I take them home with me. I also try to pick up as much brass/steel as I've laid down. It might not be my casings that I'm removing, but if I fire off 200 rounds, I try to take at least 200 casings with me. If you use a magnet to pickup steel casings, it's ridiculously easy.
2. Do a little extra. Everyone once in a while, when I don't have a full dance card of pressing, need-to-test-fire projects, I will do my shooting and take an extra garbage bag with me to pick up other guys' abandoned targets, mostly the hard to bio-degrade stuff like plastic.
3. Don't start fires. Easier said than done, but I take an extra water botle during high summer just in case.

Basically, as with any environmental issue, taking care of what's your responsibility is the key. I don't sweat the lead that I leave in the hill side.