Use Handicap Stones
Advice on playing high handicap games as Black 
Use handicap stones when answering a corner approach
But in a 9 stone handicap game answering with the diagonal attachment at is better.
is a severe move, it claims the corner preventing White to play at c and pushes White towards the marked stone.
White answers with .
is a joseki move when the marked stone is in place.
strenghtens the corner and links with the left side star stone.
White would like to extend to the marked stone or at it's vicinity, making an ideal extension from and .
But White can only extend to resulting in a overconcentrated shape.