My Buddy

I have a one year old terrier and unfortunately I have to leave him in the wash room when I leave for work about 8.5 hours a day. For a while he did wait until I got home to go out. Just recently he started using the restroom in his create. How do I stop that behavior? I take him out for about 1 hour before I leave in the morning. I have have the create open and he is not locked in, but cleaning up everyday is driving me crazy.