As far as I know, nothing really will get rid of docks and nettles for good. Nothing chemical/commercial/whatever. Goats are good for keeping the stuff in check - but won't eliminate it altogether, either.
If it's not too big an area, I would just go in again and again and cut it back, to weaken it considerably. That is, if goats (for grazing down) or pigs (for uprooting - or preferably both!) isn't an option. (Think of all the wonderful nettle "tea" you can make... I wish I had some clean nettle available here!)