Too many Sassafras seedlings -- HELP -- I'm losing the battle
I have an area about 50 x 100 feet that once had several large sassafras trees, and now has a huge number of their offspring. I am trying to create a woodland-ish garden with the anchor of a large maple tree, shrubs, eventually perennials, etc, so I am tryign to gradually clear out sassafras and nasty rose-like briar patch and put in what I want. But we can't seem to eliminate the sassafras. The most difficult ones are sprouting from underground sections of old root system. It's impossible to dig them up, and it seems that the more we try, the more saplings pop up the next year.
Anyone have any advice? I really want to stay organic, however I'm just about to give up and put on some herbicide. I've read somewhere about painting Round Up directly on newly cut stems. Or some hope that repeated backbreaking digging will eventually get rid of them? Please help.