I've been a trainer for 20 years. I respect the training that goes into medical service dogs. I can't imagine trying to take Sam anywhere pets aren't welcome, as a psychiatric assistance dog without having a very good reason for doing so.
I didn't even think about attempting it, even after he started alerting on my panic attacks, until someone directed me to a list of psychiatric alert dog tasks and I realized I
needed about 3/4 of them. And even though I'm a trainer myself, I'm not a pet dog trainer, so I'm asking a friend who's APDT certified to help.
When I started thinking about it seriously, I sat down and considered Sam as if he were an "outside" dog in for training. My main concern was his weaknesses. He's a teenager and a little protective of mommy - priority one. He's a working sheepdog and at the stage where he'll ignore a recall if he reallyreallyreallyreally wants to go herd the sheep (only an issue at herding competitions, but still). Oddly, though off leash manners are nearly 100% because of his herding training, his on leash need serious rehab -

!
Then I compiled the list of formal assistance behaviors we'd like (I consulted with the rest of the family also). We prioritized these. The family was a big help here.
One or two I thought would be good, my hubby nixed altogether. He moved one up the list to the first tier - get a drink from the fridge. He'd noticed if I get something hot or cold to drink it "reconnects" me with the world.
The point is that this stage took an entire week. I am training a specific "serendipitous" dog, fitting a dog for the job instead of finding a dog that would fit the job. I recognize this makes it a good deal harder and there's a huge potential for emotional letdown.
But I have a good reason for "upgrading" one of my own dogs - his proven record as an actual alert dog, a feature of his personality and instinct rather than a 100% trainable skill. From my experience with herding working dogs, it's seldom I'd advise using a "found" dog in such an important function.
Lo, she doth ramble muchly!
