It is ok! We are both learning!
Frog song actually solos. There is no counter that Kakazu has against it.
Actually he has a few (hope you do not mind im not gettin scans as you are a fan of jiraiya)
As you know the song does not instantly take effect before putting the victim in a genjutsu, alot transpired in between when it started and when it ends, So one counter would to be
Here is a description of Kakuzu's wind style
A tornado-like mass is compressed until it has a very high density and is then released. The wind pressure is raised to its highest limit,
There's no doubt in my mind that the jutsu would make a noise loud enough to block out the frog song, Especially if its in an open area like where this location is
Another counter is for Kakuzu to simply get on the back of his wind heart and fly high enough so that the sound will not reach him (which is what happens when you are moving in the air)
The last would be that if he somehow did get caught, One of his hearts could simply kill Kakuzu taking away one of his hearts but negating Jiraiya's victory..Not to mention that Jiraiya would most likely kill kakuzu himself then allowing him to revive..