Move it into a container, quick!! Actually, when we moved into our present house there was a single patch of rhubarb about 6' x 4' that appeared to have been there for 100 years. It took a JCB to get the huge spongy root out (back-hoe, Clanad!). And if you leave any of the root in, it'll come back. Wet, dry, sunny, shady, almost impossible to kill off. One time my dad cleared rhubarb from a garden by throwing the bits over a hedge onto waste ground. Some landed in the hedge. The next year they happily sprouted - in mid-air!