I carefully dug the whole plot a spade and a half deep and removed every bit of root I could. Then I dug a spade depth trenches every 4ft and filled them with woodchippings, leaving permanent beds in between. I limed the whole plot including paths with the maximum amount of lime specified. Then I cultivated as normal. I check for marestail regularly and tease out any I find with a small fork. I never walk on the soil, which helps the drainage. And I lime twice a year. A lot of work but 18 months later and I rarely see marestail any more.