You can also use a hair net, put the fern on the nut, then place the hair net over the fern and then put the net under the bottom of the nut (so the fish cant get in) tie it with string, and cut out the net where the "door" is and the burrie the net theys on the bottom in the sand/gravel to stop the nut floating away our the fish getting stuck. just make sure there is no loose net for any one to get caught up in. hope this helps.
-Rust
-Rust