My 5 month old Mini Aussie has started chewing on the drywall in our house. I caught him once. His little nose got swatted, he was told NO, BAD DOG!... and he was put outside. He didn't do it again for about 4 weeks. Then tonight I saw another spot. He has more than enough "DOG CHEW" toys. Has anyone else had this problem? Any suggestions to stop this problem?