What's the best way to remove/eradicate fortnight lilies? I planted a few in my front yard about eight years ago and they've just become such an eyesore because of how much they self seed. I did my best removing seed pods to prevent the mess, but I would still miss a few and now I've got little seedlings popping up everywhere and it's driving me bananas. I want to remove the fortnights and replace with a less invasive plant, so something like Ground Clear isn't an option.

Ideas?

Thanks! :)