Cotton is good and it will rot and by that time,the java will be clingin to the rock.
Or you can get a nice clump of fern and wedge it between a crack somewhere,if u find it keeps floting up you could weigh it down with weights.
Ive found that within a month,its nicely attached
One odd thing ive found, that is,with low lighting and no c02,my ferns were producing loads of little tiny plantlets on the end of the mature leaves,but since ive moved up to a high tec tank,i hardly get any little plantlets.
Maybe under low light,the plants are more stressed and put out the young plants quicker? you know like keeping a flowering plant in a real small pot,itl flower like crazy.