I have visited a place called Kirkconnell House in Kirkcudbright, Scotland where there is a double-walled field called the "Scottish acre." Apparently a Scottish acre was 'as much as man could plough with an ox in one day.' By the way, the double wall around the field had out-crops in which fires were set in order to heat the inside of the field, thus enabling the owner to grow tropical plants and fruit. Merv. Rowan