What the renters don't realize, when they complain, is that not everyone is "like them". You want to know why landlords don't rent to dog owners (it's getting increasingly difficult to find a place that will rent to people with pets)? Because some renters let their dogs destroy the house. You are coming up against a lot of really awful people who ruin it for everyone.
Friends just got a second dog, a puppy, and plan in a few years to get a third, so when one of the dogs passes away, the other two won't be lonely. I personally suspect it is more the wife's issue than the dogs', but they did post pics of the puppy on FB so qualify for this thread.
Apparently they have a 1-dog clause in their rental lease for the house they are in, so I asked, and they didn't tell the landlord until they got the puppy, realizing they might have to find a new place on short notice if the landlord kicked them out. Mind you, they had been on a waiting list for this dog for maybe a year or more, it is from a place run by monks, but they didn't look into housing options. Fortunately (and wisely IMHO) the landlord is apparently going to just charge a bit more rent, they have been good tenants for years now, and I doubt the place will be any MORE trashed by a second dog than the first, they aren't anything like Grim Squeaker's people, they just aren't super meticulous about cleaning or organizing. Personally I would have considered negotiating the rent in advance of getting the second dog, when they had a bit more leverage. . .
When DW and I were apartment hunting when we moved a few years back, one place the real estate agent showed us was a small house she owned, and she wouldn't even go in the finished basement because it smelled so badly of a cat which had "health issues". She said she would replace the carpet if we rented, but no thanks.