Dog Days by John Levitt

Mason used to be an enforcer, ensuring that suspect magic practitioners stayed in line. But now he scrapes out a living playing guitar. Good thing he has Louie, his magical...well, let's call him a dog. But there are some kinds of evil thateven Louie can't sniff out. And when Mason is attacked by a supernatural assailant, he'll have to fall back on the one skill he's mastered in music and magic-improvisation.

Started out fairly slow, i wasn't sure I'd like it at first but it sucked me in and now i want to find the next in the series.