Secure the property

Now honestly, who talks can be helped. Have you even talked to the neighbors? What about other houses in a comparable situation? After all, you mentioned 50 owners. I don’t know how a forum is really supposed to help. How about at least photos and sketches as well as excerpts from the declaration of division?

These are all thoughts one has before making a purchase; one could also possibly have included a clause in the contract specifically addressing this tendency or problem. From a distance, one cannot judge whether the other buyers are restricted in any way. Perhaps you did not have to buy. The dog/fence issue is weighed beforehand. You still have the option to set the fence 1.5 meters away from the property boundary and to plant shrubs in front of it, that is, behind them from your point of view, as a privacy screen. Edit: How a lawyer is supposed to help you is beyond me. Regards

It may only be 100cm high...

Is there a development plan that specifies this, or is it only stated in the declaration of division?

...the areas ... may be paved within the framework of what is permissible under building regulations, in particular with slabs or paving stones.

This only refers to the surface design of the outdoor facilities and is irrelevant for your project.

I would therefore like to have stones with a height of 40 cm set directly on the 60 cm sidewalk lying under our property in order to then put up a 100 cm fence on top of it.

Then your enclosure would be 1.40 m high and at least according to the declaration of division not permissible.

Is something like that permissible under building law?

Enclosures are permitted up to 2.00 m according to the Hessian building code. I have not found a restriction like in NRW limiting it to 1.00 m on public traffic areas for Hesse. If there is no development plan or if it does not include any provisions, I see no building or planning law objection.

Is a wall made of stones an enclosure?

yes

Or a paving?

no

Is the 1m calculated from the property height or from the PATH?

If I understood you correctly, the terrain is modeled so that the height difference between the property and the fence is compensated by a slope. Accordingly, a fence erected at the foot of the slope on the property boundary would be 1.00 m high both towards the path and the property, since the higher level is only reached at a distance of 1.5 m.

I often read that properties may have a slight slope.

In what context do you read that? Building law, planning law, topographically, in the sense of "are allowed"?

That is stated in the declaration of division that the fence may only be 100cm high. The building authority allows the 120cm mark.

Even if I pile up the L stones, do the 100cm still apply? Because I think I have never seen anyone put up a fence if only 40cm of it shows from their own property. But the dog easily jumps over it and that is kind of my problem.

The higher level is reached at about 1.5m distance, that's correct. Behind the fence the slope then starts... it really looks bad, in my opinion.

In our building plans and purchase contract or in the declaration of division a slight slope is mentioned. We had assumed that beforehand. That a height difference of 60cm from the house to the path (4.5m) would be reached, I could not have foreseen. The property was normally flat...

Leveling the property would give me the property that I had imagined. That's why I just wanted to have it clarified now, and since you say that piling up with L stones means an enclosure and not a stabilization, that is an answer I did not hope for but at least now I am clearly wiser.... ;(

The building authority provides the 120 mark.

Where does the building authority get this mark from? Are there any indications of the reference point here?

that a fill with L stones means an enclosure and not a reinforcement

Sorry, I overlooked the small l in the L stones. A fill with L stones is neither an enclosure nor a reinforcement, but a structural installation. Its construction should be clarified with the building authority, as it could be inadmissible on the basis of the following paragraph:
§9 HBO
(2) Structural installations must be harmonized with their surroundings in such a way that they do not disfigure the street, town, or landscape image or disturb its intended design.

Therefore, I agree with : First consult the building authority, then the owners' assembly.

I also agree with that.

Our building plans and purchase contract or the declaration of subdivision speak of a slight slope.

As Yvonne has already written, an assessment is difficult without knowledge of the entire text. If the property has a slight slope, in my opinion this statement is not wrong due to the 1.5 m wide embankment strip. I also don't believe that a legal dispute would get you any further, but the advice of a specialist lawyer might give you the feeling that nothing improper has happened.

Well, we feel not only miserably advised by the developer but also taken for a fool. I do not want to start a legal dispute, by no means, but simply want to be reasonably informed, even if in the end I have no chance of getting a decent plot of land.