Bulldog aggression towards objects and now my wife

Question
Hi. I have a 7 year old bulldog named Arthur. I have had him since he was 8 mo old.  When he was about 1 he started developing a hatred for cardboard boxes. He would do whatever he could to destroy them, even would try to jump on the counters. He never had a traumatic experience with boxes and This behavior was never encouraged.  Boxes were never given to him to play with, nor destroy.  The situation subsided somewhat in that it stopped happening all the time, however the behavior has gotten worse over the past 1.5 years and more frequent. The targets of his anger have also now expanded to paper/plastic grocery bags and anything delivery (especially pizza).  Now he will actually bite at who ever is holding an object he hates in order to get at it.  He has broken skin 1 time.  When He becomes enraged, nothing snaps him out of it.  We recently instituted the use of a crate, at the advice of our trainer, to avoid a bad situation when we bring boxes/bags inthe house.  He likes it and it does help a bit
Although it is rare, Arthur has been aggressive with my wife. One time actively persueing her after she reprimanded him (while she was pregnant-thank god no one was hurt) and most recently growling at her in the kitchen while she was putting away our Chinese takeout.  Art also has recently started going after our15 y/o yorkie who he previously paid no mind.  He never demonstrated aggression towards people/ animals before 2 years ago and has never been disciplined physically.  He does suffer from a chronic ear infection which i clean daily.  I know this sounds horrible, but 99% of the time he's ok.  Its just that 1% of the time when he snaps.  It's like he's a different dog. With a 5 mo old infant now in the house I am scared for my family and for him when I'm not home.   I'm sorry about my rameling, but I tried to be as concise as possible. Id appreciate any advice you can offer  Thanks for your help.

Answer
Hi John -

Sorry to hear that Arthur is giving you trouble, however I am sure you cannot go through life without having cardboard boxes and grocery bags in the house so here is my advice if this were a dog I was personally training.  Since you got him at 8 months old it is possible that he could have had some traumatic experience with a cardboard box.  Puppies have a fear imprint period from 8-11 weeks old and then a second one from 6-14 months old (tied to sexual maturity.) Another thing to remember is that dogs interpret sounds, smells, and objects differently than humans so what may be no big deal to us may scare your dog.
I am glad you are using a crate.  It gives you the opportunity to keep him confined when you bring the objects into the house so I would continue doing that, however, you need to start short training sessions to desensitize him to the objects.  If Arthur knows the Leave it command you can use it the second he fixates on the object.  When he looks away praise him and treat him for ignoring it.  If you are consistent with the leave it command he will soon learn that snapping, snarling etc. at cardboard gets him corrected (no, eh eh)and ignoring it gets him praise, belly rubs, treats, toys etc.  Think about Arthur's favorite things and use them as rewards for offering the right behavior.  If you are consistent he should soon start to equate cardboard boxes with rewards and this behavior should resolve itself.  Remember to work slowly with Arthur on leash when introducing or exposing him to the objects.  You can place the object on the floor out of his reach and work on the leave it command.  As he improves, start moving it closer to him and continue with the leave it.  Once he is a champ at the command and not reacting to it, try the exercise off leash and move it closer as his performance improves.  I love the leave it command because you can use it on any forbidden object, shoes, roadkill, people, other dog's feces, etc.  I recently taught a cock-a-poo the leave it command who was chasing cars on walks.  Her behavior has improved drastically and the owners are very happy.  Give it a try, and remember to really praise Arthur (lots of yays and good boy in a high happy voice) when he doesn't go after the object.  If you need help learning how to teach him the leave it command (you teach it with treats and then apply it to objects) I have included a link to get you started.  Best of luck with Arthur...keep me posted on his progress.

http://dogs.about.com/od/basiccommands/a/leaveitcommand.htm