How do I stop roots from sprouting in lawn/garden

Question

I cut down an unknown tree in front garden and taken stump out but the roots which have spread over the years are sprouting through next door lawn and also mine although I have dug most of the roots out

Answer 1

Its a common problem with certain tree species that have a survival mechanism of suckering from the lateral roots and even root fragments when the parent tree is lost.
What would have been more effective is to poison the stump immediately after cutting, with a systemic herbicide that translocates throughout the root system . But its too late for that.
All you can do now is to make it a weekly ritual to search and destroy, cut and spot spray the cut stumps of the suckers. Eventually, without sufficient foliage to photosynthesize sugars, the roots will die and stop sprouting.