Tent task
I think that this is the most genius marriage prep advice that I’ve ever heard. I have far too many childhood memories of being stuck inside the car in a rainy field, listening to my parents argue about how the tent they borrowed is meant to be put up.
Issuing every couple with a tent at their engagement party and instructing them to try and put it up successfully before they tie the knot is by far the best way of assessing suitability. It will also help massively in building patience and perseverance. You’ll also get to go on holiday – if you consider camping to be a holiday.