I’m also having a bit of trouble, just without a sketch.
Basically, it needs to be clarified: if he does it that way, would you have any disadvantages? Who maintains it? Who covers the maintenance costs in the long term? Maybe the neighbor will sell someday and the next owner says: uh, why should I do anything? It’s on your property, please take care of it! So if anything, I would define the legal relationships accordingly.
If it restricts my property rights in any way, then I would reject it. And if you don’t yet know how you plan your outdoor areas and whether these L-shaped stones might be disadvantageous for you, then I would also tell the neighbor that. That I want to wait until you know how you’ll design the outdoor area, because you don’t know yet, and only then will you be able to make a decision. He’ll just have to wait that long. And if he’s as grumpy as it sounds, well, you can certainly tell him that tone makes the music and with THOSE tones the willingness to cooperate doesn’t exactly increase, right? :cool:
Otherwise: if it means no restriction for you (or even an advantage): why not! But as I said: I would then make sure to define long-term maintenance.