I have leylandi conifers which run round my front garden and they are about 12ft high, some of the roots have come up in the lawn. I want to re dig my lawn and lay a new one, i know i will end up ripping some of the roots up and was wondering if it is likely to kill the conifers, i know the best thing is to dig the lot of them up but they give a good bit of privacy, i would like to cut back to within about 2ft of the stump.