I have one tall java fern that simply would not root on its own, so I rubber-banded it to a rock. It's still not rooted, but it's doing just fine.
After almost four months, my little fern is finally loosely rooted. It can take a while...
I also have a floater, really a leaf that brokeaway from the tall one, but it's got such a good-sized plantlet on it that I didn't want to throw it away.
Susan