I would first find out what is allowed and what is not at your place. And then one can think further about whether something dead or alive should go there.
Durable and low-maintenance, clearly a hot-dip galvanized wrought iron bridle. And for posts, perhaps something built from clinker bricks. That would also be our first choice. Visually, a beech hedge fits particularly well behind it, but it would be too much work for me. Gabions are out of the question.
Nice L-stones.
These things have been explicitly mentioned in the text of our development area regulations. Of course as an exclusion (gabions as well, thank God)