Yes, you have entered teenage years! Rebel hit that phase about 8 months and it lasted until....well....it still rears its ugly head sometimes and he is 2 years old
We have been in obedience classes since he was 4 months, so it wasn't a question of command observance. Rather it was his intense desire to drive 'mommy' wild! He would get this wild eyed look and tear off running. He would not come to me when called (by ignoring him and walking away he would lose interest in everything but me), he would dig (a pond around the ac unit), he would grab stuff off the counter (muffins, telephone directories, bills, paychecks, etc) and in general be a badass beastie! On a positive note, he never chewed my shoes, pooped in the house or barked incessantly.
I must admit, that while his behavior drove me to distraction sometimes, he was so amazingly sweet and cuddly that I never got too upset with him. If he got something he wasn't supposed to have, it was my fault for not putting it away. If he ran away while in the park, it was my fault for not having him on a lead. If he was overly exuberant, it was my fault for not exercising him enough. Looking back I DID lose about 5 pounds during this time, probably from ensuring I had a sleepy teenage Boxer!!!
Even now, at a ripe 2 years, Rebel can still get into a heap of trouble. Only now, he has his rescue brother Blue, and any number of fosters to help him :D Suffice to say, my landscaper is about to give up on me, if I ask him to re-lay drip lines again!!!!!
Enjoy your beastie!
Marnie