Can you tell me what kind of rocks plants like anubias and java fern will adhere to? I'm thinking lava rock would be no problem, and then maybe rough granite and things like that. Will they adhere to smoother rocks?
Anything rough should work. Lava rock would be fine for either. Anubias are slow growers, so it may take them time to firmly attach. Once they do though you had better hope you never want to move it.