The best way to kill bamboo is to drown it. Bamboo does not live for long if it's soaking in water. One thing however that you might consider...You can donate the Bamboo to study groups such as the Horticulture club at a College, and most probably you will even get some students to dig it up. The other option is to dig a trench around it and place a rhizome barrier so that it doesn't keep running, which sounds like the problem you are having.
If you do choose to donate it, contact me and I will do the necessary. Must be in the Northern California are within 30 miles North or South of SAn Francisco.