I've heard glu comes highly recommended, however i used tacs (pins) in the end. Pinned the roots to the wood where i wanted them and the flat head of the pin lightly pressed down on 3 or 4 roots and it held them in place. Although it looks a little unsightly at first i found it to be quite usefull, just got to remember to take them out after a few months. Also don't use ones that'll rust!
I've used sowing threar before, because i didnt have fishing line, and that fails miserably. They keep disintergrating in the tank after little more than a week sometimes.
I think i might give glu a try soon though, as i'm running out of ideas and i like to try new methods.