Replacing Retaining Wall and Putting Fence on Top Information, help and advice on many architecture, self build and design problems and issues

[Waza]

The higher ground level is 0.80m to 0.85m above the lower ground level.

We would like to replace a retaining wall that is already there.

We would then like to put a 1.8m fence on top of this wall.

We would like to drill fence post holders into the top of the wall if possible, but want to check that is ok.

How deep must the foundations be?

How wide must the wall be? The present wall looks too thin to us.

Do we need anything like ties?

There are no drains etc in the area.

[Waza]

More Info:

We might increase the height of the wall to 1070mm, but the mud remains at about 850mm, which could lower the fence.

We were thinking of using 2 breeze blocks 140mm wide each, so that would be a width of 280mm + cement in between.

We are in firm clay.