JustinN said:. So far I've found this running as far as 18 inches deep at this point.
I doubt putting bricks 1 foot down will stop them, it's more likely to give them somewhere to secretly hide and multiply making it even more difficult.
I would attempt to put something like thick impenetrable 3 feet barrier down but that might not stop the roots if they can travel deeper. You should be able to get some sort of barrier which is made to contain bamboo roots, usually a very thick plastic which would deflect the roots.
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