A lady from the Australian Shepherd rescue came over today to do a "temperament evaluation" to figure out where or if they could place him in a foster home, and we were actually really encouraged by her. The whole weekend, actually, was really encouraging. Casey was really good and fun all weekend, and the lady this afternoon talked to us a little bit about what might be making him do what he does, based on his herding instincts and his breed, as well as what we know of his history. Understanding him more is making us more optimistic about keeping him. As a bonus, we discovered he's good with other dogs and playful towards them. She had brought her own aussie to test Casey's reaction, and he "passed" with flying colors.
Josh said he'll give it another week, and seems more hopeful after listening to her, so we'll see what happens. If he improves, he may stay. Regardless, we had a great weekend. Thanks, everyone, for your emails & comments. I really appreciate it.
(Except for the one comment with a virus. I enjoyed that about as much as I do repairing plumbing fixtures, which is another project slated for the near future)