Neighbor wants to plant Bamboo hedge- can't convince them otherwise

I am a landscaper who offered to do some work for my neighbor. Turns out they want to plant a bamboo hedge along their front fence line- they've had the bamboo for a few years in small pots there already and it's not doing well (obviously).

I CANNOT convince him to not plant it. I have tried. Also if I don't do it, I'm sure he will find a guy who will and do it badly. I also have to mention this person is older and will not be around or will sell the house before the bamboo has turned into a major problem (sidewalk, water line, MY yard, etc.) which is really frusterating.

I'm in the position now where I can mitigate the damage by doing root barrier, or planting in larger pots and actually taking care if it instead if someone else fucking it up.

A description: front yard slopes into a kind of ditch behind the front fence along the sidewalk and he wants me to bring in some soil and plant the bamboo hedge to level the ditch up a couple feet. I foresee an incredibly damaging bamboo root wall to sidewalk, water line, etc in the future, not to mention it will definitely make its way into my yard (on grade with neighbors yard) in 5 years even though he thinks if i plant it "away from my yard" that it wont make its way there.

I need to look at labels again but I think it is Golden bamboo which is a runner. Stalks are golden color.

Ideas:

dig down a put in root barrier that I know probably wont work well

buy massive plastic pots (like 20 gal) from farm store and half bury them- bamboo will still creep its way from drain holes in bottom?

Any other ideas?

TLDR; Neighbor planting bamboo hedge whether I do it for them or not- trying to mitigate damage

UPDATE:

Hey just wanted to thank everyone who responded and really reinforced my feelings about this. I just had a frank discussion with neighbor and pitched the large pot idea. They were game for it and I'm STOKED. Won't look fancy but I should be able to make the bamboo look nice this summer and the area will certainly look better than it already does.
I was very thorough in my explanation of how bad of an idea, what damage it would cause, etc and also pitched our hedge height bi-law. It all worked, i think they just want it to look better than it does, but I really put my foot down and just straight up refused to do it any other way.