Hi we have a Lakeland x or as i call it yob dog !!,(he is not the dog in my avatar hes in my pics)He was just like your dog he would run off for hours,and as you said he needs the exercise,but would not recall,so i bought a 30 ft lead and started again with his recall,after about a week he would recall every time,another thing i did and still do is not talk to him at all while out,unless it was to recall him,and now when he is off lead running,every now and again he will just stop and turn round to see that i am still there
Good luck,