[Grammar] in spite of failing

[Oceanlike]

Is my sentence correct?

(a) Robin refused to quit in spite of failing the course three times.
(Somehow, it sounds a bit strange not to put 'his' before 'failing'.)

(b) Robin refused to quit in spite of his failing the course three times.

I find that my using of 'in spite of' is sometimes unsure; I'm not confident of it.

 

[Rover_KE]

I would only use (a).

 

[bubbha]

Both (a) and (b) are correct, but (a) is far more natural in my opinion.