Auto Quarry Boundaries

local fence_slot=3

local function refuel()
    turtle.select(1)
    turtle.dig()
    turtle.place()
    turtle.suck()
    turtle.refuel()
    turtle.dig()
end

local function restock()
    turtle.select(2)
    turtle.dig()
    turtle.place()
    for i = 3,15 do
        turtle.select(i)
        turtle.suck()
    end
    turtle.select(2)
    turtle.dig()
    fence_slot=3
end

local function placeFence()
    turtle.select(slot)
    while not turtle.placeDown() do
        if slot<15 then
            slot=slot+1
        else
            restock()
        turtle.select(slot)
        end
    end
end

local function forward()
    if turtle.getFuelLevel<50 then refuel() end
    turtle.select(16)
    turtle.digDown()
    turtle.dropUp()
    placeFence()
    local moved=true
    while moved and not turtle.forward() do
            moved = turtle.dig() or turtle.attack()
        turtle.dropUp()
    end
end

local function setQuarry(a,b)
    for side=1,4 do
        sidelength = a
        if side%2 ==0 then sidelength = b end
        for i=1,sidelength do
            forward()
        end
        turtle.turnLeft()
    end
end

setQuarry(500,500)