The annoying, prophylactic h6
One idea would be to pin the g pawn and take the h pawn.. There are also interesting situations created when you pin the f pawn on the diagonal. Or sometimes if you're really well developed you can find a sound sacrifice. In any case, don't let that move bother you. If he's playing it every game, regardless of the position (as opposed to doing it for good reason , due to a specific position), then he's actually helping you out.
Get the book "Logical Chess, Move by Move" by Chernev -- he's got plenty bad to say about such moves as h6. Plus "at your level" I think you will generally improve from this book.
Just think of it as a wasted move by your dad. Focus on getting your pieces developed and then annihilate him.
There is no direct refutation oh h6 in most positions however there in no need: it weakens his pawn structure,wastes a tempo and makes his king more vulnerable. Solid development will most likely prove this o be a mistake. Don't misunderstand though in some positions h6 is strong, however it is definitely overplayed at the sub 2000 fide level.
Here's an example of an opening stage:
That's a horrible example, 3.Bd3 blocking White's queen pawn -- in fact he typically plays 3.d4 and then Black has no time for ...h6? or ...a6? as he is threatened with the loss of a pawn
Sometimes h6 is a weakness, but other times it can be quite helpful; one thing is that it creates "luft" for your king.
One way is to castle on the opposite site and start a pawnstorm, when h6 is a target that makes it easier to open files.
Rarely it is also possible to sacrifice a bishop or a knight on h6 to open files.
capablanca calls it an excellent position in his chess primer, he even says it is as good as if not better than an untouched castled position against average players
The three pawns by the castled king are like the king's bodyguards. The further they move away from the king, the more vulnerable he often is.
This is why you'll often see, in high-level games, the attacking player trying to provoke his opponent into making a pawn move on the kingside—it can often turn into a weakness, or even the target of a knight or bishop sacrifice, to blow open the kingside. :D
... h6, too, can be especially dangerous for black when white castles queenside.