Last July I was given a 9 week old male kitten that was raised outside. I brought him home and successfully trained him to use the litter box with no accidents ever. I have the litter box in my bath tub that never gets used. He is a very good cat, but after he does use the literbox, he is really obsessive about covering his waste. He does this for 4 -5 minutes scratching at the box and the sides of the tub. He is 10 months old now, is there something I can do to stop this behavior?