My first suggestion for the nipping/barking when you leave/walk out the door... would be to de-sensitive him in a way to you guys leaving. Begin to pick up your keys, and NOT leave, just carry them around with you for a bit. Pick up your purse, put on your shoes, all the things you do when you leave, start to do them and then not really leave. Jingle your keys and give him a treat, make all of these associations of you
leaving into a
positive!
I would also carry treats with me alot and have him learn to sit calmly (he can't just be "sitting"... he must also be in a calm state of mind). Never leave a dog in an anxious state of mind. Practice simple commands such as sit, stay, wait, leave it, etc. Basic obedience is necessary in my opinion to live fully happily with a dog.
I would highly suggest taking him for a walk if it's possible BEFORE you leave. Leaving your dog in a tired state is usually best if he's messing/destroying things while you're gone. Exercise is very important for aggressive dogs, as well as dogs that suffer from seperation anxiety (which is what he sounds like he has... that, or he's just bored!
) Give him a fun activity to do while you're gone... get a Kong toy, fill it up with treats, or get any toy puzzles for him to have to figure out while you are gone.
Also, I'm gonna relay a "Dog Whisperer" message here (Cesar Millan, National Geographic Channel, if ya haven't seen him). Dogs need exercise, discipline, and
then affection (in that order). An exercised tired dog is a happy dog in my opinion! Dogs are pack animals, and they have a primal need to walk (not just run in a backyard) with their owners/other dogs.
I always suggest watching Dog Whisperer on National Geographic and It's Me or the Dog on Animal Planet. Both great shows!