Why doesn't my bull dog listen?

I have a 5 month bull dog that I'm babysitting and he's extremely stubborn. He's likeable but I can't get him to stay off the furniture. I have him in his cage right now. I don't want to hit him, but every time I pull him off the furniture he gets right back on it almost in defiance. Help! And he has adding jumping up on my bed. I really want him to stay off the furniture. Otherwise, he's a great dog. I told his owner that I'm going to train him to stay off the couch. How do I do that?