The Soviets used to do that with their "fishing fleet". We would send submarines out the Strait of Juan De Fuca, it would drop down to 1,000 feet, and the "fishing boats" would lose it every time. It still didn't work. I don't know of any reliable way to find a submarine, even today.
On an interesting related note, during the recent Russian occupation of parts of Ukraine, a helpful app was created and released by "Russia" [1] that would allow pro-Russian civilians in the region to act as reconnaissance for the Russian and pro-Russian forces. Very simple; if you see some Ukrainian military, push the matching picture on the app. Your location and chosen picture are uploaded, and whoever is sitting at the other end sees all the results.
Bingo; you've turned the civil population into military reconnaissance. Are they now a valid target? They certainly don't seem to be just plain civilians anymore, but they're not lawful combatants either.
As it turned out, I am led to believe that the app wasn't a great success, but it's still a disturbing trend.
[1] I say "Russia" because I can't dig out more detail right now. Obviously company X working with agency Y or some other such.