Using gravel boards as a retaining wall

[DaveBan]

Hi, I'm planning on putting up a fence (with concrete posts) & the neighbours garden is 2ft lower than our path.

I was thinking of using 2x 1ft high concrete gravel boards (6ft long) which would act as a retaining wall.

Would this be suitable? Would it be safer to put, say, 1m concrete spur posts in the middle of the gravel boards (every 3ft on the neighbours side) to help stop the boards from bowing? I'd also thought about cutting each gravel board in two and putting a small post in the middle, so effectively they'd become 3ft panels. Or, alternatively maybe double up the gravel boards so they'd be twice as thick. Or any other suggestions?

I'd really appreciate any ideas.
I've added a pic to help explain the situation. Thanks.