General(ish) retaining wall and concrete questions

Hello all--

Long time lurker who has had many, many questions answered just by perusing these threads.

Long story short-- those pink pavers where the foundation of an old aluminium shed that the house's previous owner had and I recently removed. Around the pavers is concrete (the whole back yard is concrete) and to the left and right to the space are retaining walls. Here are my dilemmas:

I want either pour concrete where the pavers are now or build a small deck. Either way, I have that space where the wall on the right side ends (originally, the shed acted as what kept the soil from shifting) and the unevenness of my yard and the yard of the neighbor behind me (you can notice that there is exposed soil under the fence)

So as to my actual questions-- if I were to continue the retaining wall on the right until it 'connected' to the fuller wall on the right, would that sufficiently keep soil from shifting from my neighbors property? If I were to do that, would pouring concrete add more reinforcement? If I were to pour concrete, would I need to stake things out on only the left and top portion (along the new retaining wall)? I'm at a bit of a loss as to how to put concrete in that portion.

I'm a bit perplexed as to how to proceed-- I have a feeling I am making this far more complicated in my mind that it actually is, but I figured a few opinions as to what to do would be greatly appreciated.

I am a little confused on exactly how you want to do this. Areyou wanting to continue the wall from left to right and connect it to the other wall? Or are you wanting to build a small wall in the back portion up against the fence to just keep dirt from coming through? Either way you will want to put a block in there somewhere to keep that dirt out. When you build the new wall you will want to put a small footing under it and to keep it strong fill every other cell with concrete and it won't go anywhere. Then you can pour concrete up against the wall no problem.

Let me elaborate visually.
Where the yellow lines are at, I want to put a retaining wall, essentially continuing the short wall on the left. Should a continuation of that size wall be enough to keep soil out from my neighbor's yard?
Thanks for the help!

A couple rows of allen block would do the job.

Allen block would be fine or you can match those 6x8x16's that are there but then you would want some concrete under them as a footing to hold them.

I believe most Allan block walls don't require concrete footings, unless same are required by local codes.

Allan Block are not intended to be used on a concrete footing. If you use concrete everything in their installations would not be productive and would be contrary to all of the engineering behind a segmental retaining wall block.

The same applies to all of the other national retaining wall block brands.

Dick