About 18 years ago, my then-neighbor planted hedge plants down the property line between his house and mine. I BEGGED him not to, because the guy behind me in my last house had done the same think and then neglegted them... they grew to be huge and hung over my fende.
You got it... he planted them anyway, and they grew, and Grew and GREW. Of course, he moved away, and doesn't care anymore. My current neighbor eventually had them all cut down. Cost a bundle, AND he didn't have roots removed... just chopped off at the top of the ground. Now, of course, these dumb plants keep springing back up. I have his permission to keep them chopped off (it's on the other side of my fence, and not easy to get to), but I'd like to put some chemical on the stumps (some are 10 inches across !!!) to kill keep the new growth from coming back. Is there anything out there that will do that? Before you suggest it, digging up these stumps is NOT an option. They've taken over the whole place underground - would need a backhoe to do that.