WellyWales: As said, that might give the player going first a bit of an advantage.

Perhaps it's better to have a rule that the second player cannot play his first move adjacent to the first move of the first player.

However, I don't think the second player has that much of a disadvantage - certainly less than white has in chess. Yes, the first player has the disadvantage of having to make a blind shot - but there are only five enemy frogs. He's more likely to make a shot right next to an enemy frog, revealing a non-zero number, leaving the second player to make a blind shot.