been reading up about docks and it seems there are 3 organic ways recommended to deal with it:
1. graze sheep or cattle on the land. they eat the dock leaves and as the plant needs it's leaves to photosynthesise, it cant and it will eventually die
2. introduce some kind of beetle - forget what kind!
3. dig it out
the article also said not to let the sward get too short or the docks will flourish
i think that is the way we are going to go - too much bad stuff in all these other treatments for my liking!