What is the best defense against the King's Indian Attack? How can I break the King's Indian Attack? I think my h7 square is vulnerable to attack; what is the best way to break this strategy?
I doubt that the King's Indian Attack can be 'broken'.  It's a very solid position that White takes the time to setup, if Black is not careful, White may be able to gain space on the kingside, with moves such as e5, and develop dangerous attacks if Black has castled there.

As for h7 being weak, many things need to happen from Black in order for this to be realized (such as a semi-open h-file, Bg7 has been exchanged, in which case it is h6 that is weaker), so there may not be anything there worth exploring.

I can't comment on what the 'best' defense would be, but there are many good ones, one such is the Botvinnik System.  Black makes use of the extra available tempi to set up a strong and flexible defense.  The typical structure would be pawns at c5, e5, d6, g6 and pieces at Nc6, Nge7, Bg7 and 0-0.  Black has a firm control over the d4 square and can potentially break with either ...b5 or ...f5.