Chris Manvell says:

With two rail running the operator controls the direction of the train, irrespective of the orientation of the loco, so really you are acting like a signalman. I.E., turn the controller to the right to go clockwise, and to the left to go counter clockwise. (Three rail allows you to decide whether the loco is running forward or backwards, which is true cab control.)

The simplest solution to your reversing loop problem uses three breaks in the track and four diodes. — 1N4001 (1A) or 1N5400 (2A)will be fine. The circuit can be seen at http://trains.manvell.org.uk/misc/ReverseLoop2.jpg . Note that the distances between the centre break and the two diode breaks need to be equal to the longest loco pick-up length, and that the three breaks should be as near to the exit from the reverse look as possible. (The arrangement is, in fact, bi-directional.) The train will stop once the loco has passed over the centre break, at which time reverse the controller.