@Jon S.
If you are going to allow dogs, then know that any breed can be aggressive and any breed can bite. The dog that mauled the Frenchwoman who was the recipient of the world's first face transplant was a Labrador retriever. In fact, Cocker Spaniels are relatively more aggressive to people than are pit bulls.
Dogs are like people, and every dog has its own personality. While some breeds may have a genetic predisposition to certain kinds of aggression (towards other dogs, or in defense of their owners, for example), how the dog owner manages their dog and the individual temperament of the dog matter more than the breed. That said, some homeowners' insurance companies have banned certain breeds, so be aware of your own policy when you rent to people with dogs, and/or make sure your insurance company doesn't practice breed discrimination. I have State Farm and they don't discriminate based on breed.
It's my personal opinion that children cause more damage than dogs. SO, if you are going to rent to people with dogs, then you may as well simply charge an amount for rent that you feel comfortable with for people with dogs, rather than tacking on extra fees and pet rent for a pet. You can advertise your rental as pets OK on a case by case basis. Then you make sure that you like the individual pet, that it is well mannered, spayed/neutered, clean, flea-treated, up to date on its vaccines, and has good references from previous landlords. I also require tenants to buy renter's insurance, as I'm more concerned about liability than damage.
If people in your market tend to have pets, then you will do better with this strategy than by charging all sorts of extra fees and rents. You may even have people interested in renting your unit for the price you advertised, and they don't even have pets. But non-refundable pet fees are a real turnoff to most pet owners, and rightly so. Why should someone with a dog and no children have to pay more than someone with children and no dog, in the event that their dog could cause some damage? An extra refundable security deposit is much more fair, because it doesn't penalize pet owners simply for being pet owners, AND your tenants will be incentivized to keep your unit in excellent shape so they can get their full deposit back.
Furthermore, at least in Oregon, a savvy tenant would have a legal claim for a full security deposit refund if the only damage was from pets, and you charged a separate "pet deposit" or "pet fee" that didn't cover the entire cost of actual damages sustained. At least, that's according to a landlord association here in town. Instead, just charge a higher total "security deposit," and any damage sustained by pets can be covered by the security deposit.
And while charging extra pet rent is legal and widespread, it just screams "exploitation" from a tenant's point of view. If you want to have a mutually respectful relationship with your tenants, one in which your tenant wants to stay for a long time because they feel trusted and in turn think you are trustworthy, don't come up with all these extra fees for people with pets. If you roll it into the overall rent, they won't know the difference and they'll feel grateful to live in a place where the landlord isn't apparently nickel and diming them to death.
You'll have the same cashflow as though charging pet rent, but your tenant relationship won't be built on a foundation of distrust. (And this is where other landlords on BP will feel compelled to reply with defensive comments about their pet rent, but that's OK. What's good for them is good for them, but I stand by this statement.)
Responsible pet owners are the best tenants because they are grateful to have found a landlord who will accept them, and they'll not only work extra hard to make sure your rent is paid on time and the place is well taken care of, but they will also stay a while if they feel they aren't being taken advantage of.
Just pet-proof your property and screen well. Or don't accept pets--because that's less competition for the best tenants for me.