The difficulty is explaining this stuff running stuff accurately, which is why there is so much misunderstanding. Ph aurea is a running bamboo and in climates with warm damp summers - warmer and damper than Liverpool, it is uncontrollable. In Liverpool it is cool enough that it is unlikely to do wild like it does in the Azores. I have some Ph aurea in Bucks I planted about 10 years ago and it still hasn't spread more than a foot. But i have it surrounded by lawn and can mow off anything too cheeky, so I haven't bothered with a barrier (unlike some of my bamboos I have against the property boundary where I don't want to annoy the neighbour). But it is wise to put in a barrier if you can't keep an eye on its spread so easily, or have potential to annoy someone. Barrier needs to be 50cm deep and needs to be something you can't make a hole in very easily by pressing a sharp point against it. 1mm thick hdpe sheeting is sold for the purpose.