Dig 'em out! Dock has a very long tap root which if you can get it all out, means the end of it. Of course, easier said than done, which I do appreciate as I have dock everywhere! I don't use weed killers, purely because I never have, know nothing about them or the long term affects on soil and crops, but I am sure there are some products on the market that will do the job post haste! Mind you, I heard Stephan doodeedlidum (can never remember his long and complicated name) the gardening man on TV today saying clover is pretty immune to most weedkillers, so again, maybe best just to dig? :-\