It does seem there are many theories about why they surface after a rain. Sounds like the one most of us heard about them drowning isn't necessarily the case, at least not for all worms.
This article suggests that they are using the wetter conditions as an opportunity to migrate more easily than they could underground. If they're trying to migrate across concrete, obviously that wouldn't go too well. I would think a physical barrier would be the way to go, as then they couldn't get up onto the patio and get stuck. Not really sure how tall it would need to be. I don't imagine worms are skilled at climbing, but I could be wrong. If it were me, I'd use logs along the edge, though I know that isn't everyones preferred aesthetic. Maybe mulch mounded up slightly or some kind of stones or bricks? Seems like any kind of deterrent based on scent or whatnot would be likely to wash away in the rain.
I also wonder if soil compaction caused by the patio construction and/or chemical leaching from the recently poured concrete could be increasing the issue? Maybe adding organic material like leaves or mulch to the soil around the patio would make them less inclined to go in search of greener pastures and end up on the patio, if that is in fact what they are doing? Hope you can find a way to keep them alive and happy in the soil!
“Action on behalf of life transforms. Because the relationship between self and the world is reciprocal, it is not a question of first getting enlightened or saved and then acting. As we work to heal the earth, the earth heals us.” ~ Robin Wall Kimmerer
2
