There are many versions of ruck touch with the support players needing to recognise the needs of the tackled player.
The defence should be conditioned to provide increasing pressure to the tackle area. This will develop the situation recognision of the attacking players who must play accordingly. Robotics in rucking regardles of the situation should be discouraged and the option of picking upthe ball and going forward should be an option
Notice how these players do not naturally set up rucks. Both teams try to keep the ball away from breakdown situations.
What would these games look like if the coaches stepped in and insisted on rucking?
Finally introduce live 1 v 1 tackling in a controlled environment using a channel. Standards will vary but as coaches it is important to praise all of the players. Doing this exercise too early may cause problems and refrain from doing so until the fundamental skills have mastered