What are DAP plug-ins?
I'm in agreement with tbone; our male V seems a little bit more "anxious" when his schedule is disrupted...a quick 20 minute run behind the bike seems to do the trick if we're in a hurry for some reason! A tired dog is a happy dog.
Sounds like you're going to crate him again which is a good idea. However, I do not believe crating is going to solve any problems with his behavior in the long-run if he indeed has serious separation anxiety issues - it will just prevent him from destroying your home (which isn't a bad thing, mind you!). I have a friend who's dog bloodied himself trying to, and succeeded at, digging himself out of his crate.
From things I have read, if this is anxiety induced, you will need to "desensitize" him based on what triggers this behavior (i.e. picking up car keys, putting shoes on, packing a bag). Here's a quick read:
http://www.boulderhumane.org/hsbv/go.asp?mode=sep_anx . I would highly suggest a call to a local trainer or even the humane society if you want him to be happy and even stay "calm" in the home during the day when you leave.
But, tbone also has a good point that outside stimulus could also be triggering this behavior. Thunder? Lawn mowers? trash trucks?
Good Luck!!!