If Stefan perfects a technique so that it cannot be reversed, we have to go back to the drawing board
Don't hold your breath
About the timing, I teach my students that kaeshiwaza should be applied at the very moment when tori's movement turns from avoiding the attack into applying the technique - which is the moment when tori can be said to change from defender to attacker. The aikido technique can be described as kind of an attack, so that's the moment it is vulnerable to aikido strategy, i.e. the kaeshiwaza counter technique.
So, when doing kaeshiwaza, one should pretend to be the one attacked.
Maybe that's what you mean, Joe?
When I suggest that there is some way of developing one's aikido technique so that it can't be countered, I mean that it has to be done in a way that makes it impossible for the attacker to pretend to be attacked at some point in it.
Or one has to do the technique very forcefully....