If the rocks available are shale, very soft granite(you can easily
break it with a hammer) or any other soft, porous rock, make a dry
wall. A cement wall with this material will often fail, because the
rocks will just break off and fall apart. But if your soil is a
clay, this soft rock makes a great dry stack wall. Layer of rocks,
fill in voids with loose, dry dirt, next layer of rock. Try to nest
the rock in between the rocks of the lower layer. Water the wall as
you finish each day or every time you walk away for a break.
Dry stacks follow the same rules as a wired wall, but you are using
clay instead of cement, and the wire only kinda works.
If you're retaining wall isn't really retaining anything important,
just making life easier, maybe you should build a series of smaller
dry rock walls(no mortar or concrete) and have fun planting yourself
a rock garden in each one.
Dry walls can be made of broken concrete, old tires(makes a great
retaining wall to protect the 1964 Chevy pickup on blocks, behind
the chicken coop) , logs(don't last long), concrete block (what's
the point?), rocks, railroad ties (see logs) and almost anything
else you can stack.
If your yard has rocks everywhere, great! Pick them up and make a rock wall, or place them next to each plant on the flat and call it a rock garden. If you live in Bakersfield, Los Angeles, or one of the other big cities with no rocks except by the pound from the local 'materials' company, look around for somebody removing some concrete. Broken concrete makes a great wall. It looks natural after you get a few plants growing into it.