I know people that have tried it (the spray) it doesn't work unless by accident… and you know, you need to stand in the rain with Dallas...:p Been there done that with many a puppy
Oh believe me, I was soaked! I was standing right in the rain (during the most downpour of course) in the middle of the grassy area he goes in but he just would NOT go! I even kept bribing him with treats to stay in the grass & go but he kept trying to back out of his collar to get his paws on the concrete vs. in the wet grass. I know when the sprinklers go off it's a bit more a challenge to get him to go in the grass but he manages. This is actually the first time he's been out when it's still be raining down.