Fence foundations on old foundation?

Hello dear house builders,

I wanted to start setting my fence to the street over the Easter weekend.
The plan is a wooden fence with 180x180cm fence panels on 9x9cm wooden posts. I wanted to screw the wooden posts onto point foundations. I have already procured screw-on sleeves for that.
At the border, there used to be a small wall on which a typical DDR metal mesh fence was mounted in the old setup. This was mostly demolished for the new construction, only a few pillars were left standing.
I went to work fresh with a spade and earth auger and had to find out that about 40 cm deep, the old foundation of the wall is still there. Apparently, the demolition contractor only removed the brick wall, but left the foundation in place.
I then stopped for now and dealt with other matters (distributed piles of earth).

Now I am of course wondering how to proceed.
From my point of view, there are the following options:
1) Doesn’t matter – simply pour the point foundations onto the old wall foundation, possibly going a little wider. – Risk that the relatively large fence panels will simply tip over with the foundation in the next storm.
3) Break up the foundation at points
2) Two to three holes in the old foundation – insert rebar and then continue concreting. Medium effort because the old foundation must be sufficiently exposed each time. – Is this better or does it hardly help if no really force-locked connection is created?
2b) Properly glue in the rebar with injection mortar or similar. – Force-locked connection, but even more effort/cost
3) Remove the old foundation with an excavator – greatest effort/cost, actually not desired.

I ask for additions to the assessments and possible other options I have not yet considered….

Thanks and best regards

Tolentino

The first 3) please ignore, no idea what I did there.

Attention, all just young experience and feeling!

I consider the risk at 1) felt to be acceptable, but I would still prefer to go with 2). Specifically 2c) ;)

Instead of using the insanely expensive injection mortar, just make the holes a bit bigger for the rebar and fill them with relatively thin, fine, cement-based concrete.
I also fixed rebar in the concrete wedge this way, it’s held like a bomb so far.
Although they don’t have to withstand much load.

I think this is the golden mean in terms of effort/benefit ratio.