Solo play?

[larry marak]

That or turning counters 60 degrees (i.e. one hexiside) to indicate their activation is finished.

I like Enrique's system of placing minefield counters in likely set up locations for hidden units (place at least double the counter's on the board as units to be hidden), designate 3 as a real unit, and scramble before placing on the board. Roll a die to determine which off board display unit is now on board. Not perfect, but works pretty well if you aren't counting on hidden units to be spotters.