Fissidens will take over, but it'll be awhile.
The "mini Pellia" will do well on the rocks.
It'll take time, but will look nice as that grows in.
Moss: you can also use Anubias, Buce's, Crypts.
Other nice plants that are less trimming: Downoi, Starougyne, even Blyxa is less trouble, Hygro arag, etc.