I`d start from the top and go across to the side , then step a meter down and go back across and then keep working your way down in a Zig Zag pattern,a meter at a time rather then doing the Grand old Duke of York method ,which will be VERY tiring after half an hour. The detecting going downs easy .Its detecting and swinging going UP that`s the killer bit. And unless your as fit as a Butchers Dog and only weigh 7 stone ,fatigue soon kicks in detecting up n down plus carrying your spade on acute slopes .