I have quite a problem with my neighbours bamboo which is quite a thug. It is 9ft tall and becoming very rampant, sending thumb-sized spears through into my garden. They travel about 6 inches below the surface and have quite strong roots along their length; it's a hell of a job trying to stop them taking over that end of my garden. I have tried digging them up but that's quite a task. I would be very grateful if anyone could offer some sort of solution to how I deal with this problem please.