My B5 wagon's previous owner had a dog, and despite her having it professionally detailed before she sold it to me (she felt bad, although the car was still pretty "clean"), and despite me using just about every trick in the book over the years up to calling a priest to purge the dog smell, it still creeps back.
If it sits for a few days, especially in sunny humid weather, that stench reactivates and comes back to life, LOL. I hate dog smell.
Since the car is not driven regularly, I place a tray of ground charcoal (the stuff used for aquarium filters) in the back. That seems to help at least keep the canine cologne from becoming over powering.
I think dog owners really become immune to it, just like cigarette addicts have no idea just how awful they smell.
But, the car was cheap, and is otherwise fine, so I deal with it. And I will be the first to admit, I am pretty picky about that sort of thing.