I have a 25 foot stretch of Bambusa oldhamii clumpers along my fence line that I can't let wander into the pavers I'm installing next month (these pavers cost a fortune). They're about 3 years old, and already made their way through a crack in the old concrete. I know they don't spread like runners (I already have three major sections of the yard full of runners contained with a barrier 24 inches deep). My question is how deep should I bury the polypropylene barrier? Digging the trench is extremely difficult so every inch counts. From what I can see in a cross section, they only go down to about 6 inches; not nearly as deep as my runners.

Thanks.