[cj125]

Is he neutered? How about the cat and your new pup? Some hump because they're getting into puberty. Others hump for dominence. After a certain period of time it can become a habit.

First, I'd suggest getting them all neutered (if they're not already).

Second, try to distract him whenever he starts to hump. Make a noise or squeak a toy. That will help to break the habit.

Third, make sure that you're treating them all the same. Like when you give them treats - make them all sit down at the same time and give each one a treat according to who was there first.

Lastly, make sure they all know that you're the boss - not them

Good Luck & Let us know how it goes.