I don't have a huge amount of rentals, and I have only been landlording extensively for about 4 years. When we started, my husband and I decided that we would allow pets on a case by case basis. We collect a REFUNDABLE $500 additoinal deposit (call it additional deposit instead of "pet deposit" in the lease as it allows you more flexibility to cover any damage at move out--pet deposits can only be used for repairing pet-related damage) for each pet accepted as well as pet rent at $25 per pet per month. I make it refundable so there is incentive to get it back.
My experience with this has been mixed. The first person we allowed to move in with a pet had an American Staffordshire Terrier (which I now know is a fancy term for a pit bull LOL). Luckily the dog passed after ingesting some rat poison the dog's owner put out in the yard. However, I learned later from the neighbor that the dog was a terror and she had to give her own dog away because my tenants dog became vicious and crazy in the presence of other animals--it even chewed up our backyard fence trying to get at the other dog. Although I don't wish harm to any animal, I have to say in that case I was somewhat relieved. We still have these tenants and they have lived in the property for going on four years, so I don't know yet what additional damage has been done.
We had some tenants that just moved out and had a pommeranian. No damage in that unit at all--yet we collected an additoinal $300 in rent while these folks lived there.
We have some other tenants that we allowed to bring a 90 pound Chesapeake Bay Retriever to. The unit had old (but not too bad looking) carpet and we didn't do a lot of upgrades when we bought it, so we thought making it large dog friendly would be fine. These people are our best tenants. They have beautified the yard and the house, and the house doesn't smell like a large wet dog at all:) I was impressed by that, since I can definitely smell dog (particularly retrievers) when I visit other people's homes who have them. The dog is always clean and well groomed.
I think whether there will be damage or not depends on the people.
Some things to consider:
-I am more willing to accept a dog in households where there is one person who mainly stays home all the time.
-Make sure the animal is current on all shots, etc (indicates a responsible owner who takes good care of their animals).
-Female dogs are better, as they do not mark their territory.
-Dog must be neutered.
-Meet the dog with its owners to ensure that it is friendly and can follow basic commands.
-If the people are well organized and have good attention to detail, they tend to be good pet owners in my experience--and good tenants in general.
-Write in your least that tenants must have unit sprayed and treated for ticks and fleas and provide receipt as evidence after they vacate.
That is all I can think of at the moment.