Defining an allotment border (Berlin Wall not required)

I've got a long rectangular plot which I've decided to split in half and share with another couple.  The dividing edge runs East/West.  I'd like to plant something along the shared border on my side to discreetly define where the boundary lies.  I get on really well with the other couple, there's no issue with security,privacy or the boundary itself.  I just need some kind of low green screen so someone can look at the strip of land and clearly say "that bit's his and that bit's theirs" without a row of palletts making a territorial statement or obscuring the general view.  Ideally I'd like to plant something that will grow/can be trained in a straight line, that grows no more than waist height, that can be cropped with some kind of fruit or veg every year.  Any ideas or comments?

Fruit trees as espaliers, fruit bushes as a low hedge, globe artichokes, trained tay/logan/blackberry?

I have a 25mtr length of raspberry canes that form the border between ours and our neighbours. The only problem with them is that they will send runners up all over the place.

Grapes or a herb bed,Rosemary would stay green all year & you could intersperse with lavender, it is edible,thyme would be another,sage.

I would be inclined to just have a permanent marker at each end of the boundary line, whether a post or a plant, and visually draw the line between them.

Snowdrops has already mentioned rosemary, which can make a very attractive hedge.

A series of low raised beds with herbs in them could benefit both of you, and if there are spaces between each bed you can visit each other easily too

lavender can make a lovely low hedge, it will smell great when your there and won't cast huge shadows