What made you want to look up xenial? Please tell us where you read or heard it (including the quote, if possible).
Black dog is an oft-used phrase to mean depression. Here's a link that attributes the phrase to Winston Churchill, but I suspect he didn't invent it. I like the way they described it though: Black Dog was Churchill's name for his depression, and as is true with all metaphors, it speaks volumes.
A: Yes. Training of dogs on black bears is a legal activity and one that is vital to managing certain types of bears nuisance activity in New York. The use of bear hounds is one of the most effective tools for reducing bear damage to farms, especially reducing damage to corn.