Kathy wrote:
You'll have to do what my Mum did with my Dad. She used to pick a weed,
give it to him and say "If it is not EXACTLY like this, leave it alone."
Seemed to work, though weeding took some time as he did it one weed at a
time.

Actually, I often weed like that even now, at least where the weeds are more
than a week or two old - due to the slightly different effective methods for
removal (ie, dandelions you need to go deep, straight down, twitch you need
to dig out gently and carefully to avoid snapping, creeping buttercup you
need to follow back to the source and remove the shallow-but-long roots out
of the main plant, etc)