The verb ‘to dod’ is on record from the early thirteenth century when it was used in connection with having one’s hair cut, and by c.1440 it occurred with reference to trees that had been polled or lopped (OED).
A coal-mining term; if the ‘down-side’ was the downward slope of the vein the inference may be that this was an ‘end’ cut on the ‘down-side’, parallel to the cleavage of the coal