The obvious problem with using landmarks for the circuit turning points is that you won't be able take them with you when you go to another airfield. I was tought to start the turn onto x wind at 500 ft (QFE), start the turn onto downwind when the runway is just under the tailplane and turn base when the threshold is about 45 degrees behind you over your shoulder. Wouldn't have thought there is anything wrong with using land marks as long as you remember the way you were tought initially.