Low garden wall to follow 6' tall fence

[MiamiCuse]

My property is a corner property. On the two sides I have neighbors I am building a 6' tall privacy wood fence up to the edge of the house, then on each end a gate will be installed to wrap the fence to the exterior wall of the house.

However I would like some sort of a border to continue to the edge of the property which is about another fifteen feet from the edge of the house. This border ideally would be much lower than the 6' tall fence. Initially I was thinking of a stone / masonary wall like this:

after looking at how much that would cost I gave up, now I am thinking of instead of a low stone wall, what about a railroad tie 8" tall if I stack one on top of the other that would be about 16" tall. Would that be a nice transition? From a 6' tall pine board wood fence to a 16" tall double railroad ties? Trying to imagine what that would look like, would it be too low?

I am located in Miami Florida zone 10, so the railroad ties and fences would be pressure treated. The area may be flooded, so I need a way to anchor the railroad ties to the ground. I have seen people drill holes through them and then pound rebar through it to the soil, is this the proper way to anchor them in place? or do I need to dig a trench and partial fill with sand/gravel for drainage then put the rr ties on top?

Since it is a corner property, I would also like to have a low border around the property in the front where the sidewalk curved. Obviously rr ties would not work there, any suggestions?

Thanks in advance,

MC