I had to wait a day for the rain to pass, but finally stage one is now complete.
Stage two will be the careful placement of large sandstone, butted against the bricks. And stage three will be a concrete trench against the rocks, carefully disguised with more (smaller) rocks placed inside the trench.
I'm just happy to get the plants in, as they were practically bursting from their pots. Now they have plenty of room to spread out and hold all that lovely soil together.
I have a few other projects coming up soon, so I don't know when I'll be able to start stage two of our watertank garden.