The pusher should work.
If Ralph doesn’t move anymore after the collision you must have done something wrong (that’s all I can assume, as I know neither Ralphs code, nor your changes).
Anyway, I don’t think you’ll want to use the pusher, because if you do use it, it will let your character be pushed back from everything it collides with, which would include collectable objects (if you’re planning on implementing them anyway).
So you might want to try the collision event handler.
Create different reactions to different objects that ralph could collide with.
The simplest way to achieve the desired behaviour here would be to just reset Ralphs position a few WUs (World Units) if he collides into his “enemy”.