you can actually take a sheet of craft mesh (the same kind you use for DIY dividers) and lay it out on the bare floor of the tank, and then tie the roots to it using fishing line. after that, lay down your substrate and your plants won't move, and will actually grow tendril roots between the meshing and semi-permanently implant themselves to it.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)