Staff control of layout

Considering that I am building a single track main line with a single track terminating branch line I figured that to avoid the obvious problems of trains meeting either head on or nose to tail then I needed some form of control to ensure only one train operated in a section at any one time.
The simplest thing I could think of was to use a key switch where each section would have a different key so that drivers could not enter a section that was not "theirs".
Now key switches are not too hard to get BUT to get six (6) different keys cause I need six sections was a bit of a problem. I tried Jaycar and found that by using three different types I was half way there but 6 ? well. Ebay to the rescue and with a little searching I found quite a range available and now with three (3) more different types I have the six I need to control the layout. 
With the exception of Gwabega that is a baloon loop and staging area all sections will have two key switches one at each end of the section that will isolate a section of track so that a train cannot enter or leave the section without the key/staff. So before you can leave Dunedoo to proceed to Merrygoen the driver must have the key/staff to gain entry to the section and to leave the section the driver must remove the key/staff at the entry and use the same key/staff to turn on track power at the other end of the section.
Of course the driver must have a clear signal before leaving the section to enter a locality. The driver must also have a clear signal to leave a locality and these signals will only go to clear when it is safe to proceed. (signals will for the most part be controlled from the local signal box by mechanical or electrical means.

In the case of Gwabega there will only be one key switch and a driver will need the key to proceed from Merrygoen to Gwabega and once the train has been stored the driver will return the key/staff to Merrygoen for use by the next driver traveling to or from Gwabega. Drivers will have some considerable responsibility in ensuring the safety of their trains.

There will be some interlocking (electrical) to be done to ensure safety but that's another project altogether.

Just to give an example the following photos are of the key switch to allow a driver to enter or leave Merrygoen travelling either to or from Gwabega.

The staff in place and turned on to allow power to the isolation section of the track

Staff/key in place to power the isolated track section

The staff/key removed so no train can enter or leave Merrygoen