Toggle Hidden Units not working

[Schoenwulf]

For solo, could one use the modifiable terrain marker, marked with a "?", and place twice as many of these on the board as there are hidden units as Joe has suggested. Then just roll a die with 1-3 drawing an active unit, and 4-6 a dud. Do this until all hidden units have been discovered.
When I have played ftf with Vassal online via Skype, I just gave my opponent a password-protected document with the hidden unit locations; after all hidden units had been revealed, he was given the pass code to open the doc and could verify that I had played them all correctly.