I am rebuilding my koi pond and need advice about plants under my waterfall as well as what to do with the edges of the waterfall.

Waterfall previously:


I built a container below the waterfall to plant some ferns, etc. We will plaster the layer of two bricks below the waterfall to have the same artificial rock features


Any ideas?

Then I need ideas what to do with the edges of the pond.We are plastering this weekend: (The area where the book is, was filled up by concrete this week




Thanks for any advice