First of all do you see it spreading 3 or four feet away from the main shoots? If so then It’s running bamboo. If not then don’t worry because clumping will spread some but is easily knocked down.
Disregard the answer that said all bamboo spreads that way…NOT SO!
There are 2 kinds running which is highly invasive and clumping which is not. Second answers was correct about the clumping bamboo.
the barriers have to be made of much thicker material than a couple rows of plastic and much deeper than 18 inches.
You need a rhizome barrier of 30" to 36" no less than 30mil to 60mil plastic.
Open this link and see what you have to do. Then go to the people that sold the stuff to you and give them what for!
Bamboo Rhizome Barrier
There are three basic methods of controlling running bamboo.
Aborting new shoots
Open the link and read/see photos because you need to be prepared.