Wild Lillies

So my great nemesis has begun to rear her ugly head already! The previous owner of my home thought it would be a great idea to dig wild lillies out of the woods and plant them around the house and garage. As with most things wild, I CANNOT get rid of them! I have tried to dig them out (they were very overgrown and the attempt only thinned them - and encouraged them!). They can push through the weed block (though not quite as readily as they used to grow) that is around and under my SFG. They are already showing their tips through the SFG in greater numbers than last year. They are very deeply and strongly rooted. I tried salting them and bleaching them (not IN the SFG) - which did nothing. I wanted to avoid week killers as it is right with my SFG and the food I feed my family - plus I have a 2 year old and try not to use unnecessary poisons. Any ideas?!!!? I would really like to be rid of them so I can plant MY desired flowers, etc as my landscaping (ie - butterfly attracting plants, etc).

I try to stick to organic gardening ideals & practices, however there are times when I choose to deviate from my ideal. I have found Round-up to be the best spot product as you are to spray only the plant you want gone. I followed the label instructions and was successful with one application. I have only used it 2x on very tenacious weed plants, Horsetail (Equisetum arvese) http://www.snakeylaneallotments.co.uk/articles.htm and poison ivy.
Sadly, both of these came into the garden through compost bought buy the yard/truckload.