How does creosote harm the ground water? Its nothing more than concentrated pine pitch. And I have found mothball flakes spread around your patch works well. You can even put it right around the plant. Nothing in it at all that will harm your plants. And its cheap and easy to find. Once they start putting on some resin critters will shy away anyways.
I am a farmer, and you are right, we do not want to harm the ground water. The pitch that is available to the public and us farmers is wood based pitch. About the biggest real issue with it is how to wash it off once its on you. You expose yourself to more harmfull things with the solvents some use to remove it. Now coal tar based pitch is a different story. Quite regulated and only available with a license. Even then to really harm the ground water, it would need to be a concentrated spill above a somewhat shallow aquafer to cause harm. The amount from a pile of railraod ties or the spread out poles. As far a we know now, no worries. Edit: Oh ya, I have seen Deer licking old ties before. And porcupines seem to love to snack on them.
Or possibly a road kill... Unfortunately most of our rural areas are over run with Ferrel animals. There many ways to live trap and humanely dispose of these animals. I am not advocating trap and kill them all. House pets often find their ways into traps. So think twice. But a pelt on a tree, bet it works pretty good. Gonna stink in your garden after a few weeks though. Then either you pull the stinky pelt down, or move your plants. lol Ok, have my flack jacket on now.