Many tenants think it is unfair to charge both extra security deposit and extra rent for the privilege of pet ownership and I will tell you why: If someone wants the pleasure of a pet (especially a dog or cat) an extra security deposit is nothing to pay for that pleasure. Most tenants understand that and know the extra security deposit is taken in case the pet somehow damages the rental unit. If they do damage something, the landlord pays for the damages out of that money.
Now when a landlord charges extra rent for a pet, are they charging it because the pet will be taking up more living space, use more hot water, or flush the toilet? No. They are charging extra rent because the pet could possibly cause damage to the property.
Therefore, when a landlord charges extra security deposit for wear and tear or possible damage and extra rent for those same reasons, many people believe they are being double-charged for the pleasure of owning a pet. And nobody likes to be double-charged.
On the other hand, from a landlord's perspective, charging the extra rent for the privilege of pet ownership is smart business since the risk of damage is definitely higher, and the tenant should compensate for that risk. Let's say you feel $25 a month is enough for compensation, so you add that to the rent. This additional $300 per year somewhat eases your mind should the pet cause damages to the premises.
Let's say six months into the lease the tenant moves out. Upon their departure you discover Fido had a weak bladder and consequently ruined all the living room carpet. The $150 you collected in extra rent ($25 per month times 6 months) will not cover that replacement and because you didn't receive any extra security money up front you lose.
The basic thought to keep in mind from a landlord's perspective is a pet who has a bad day can do hundreds of dollars of damage to a property during that one day and collecting $25 or even $50 per month to cover that bad day just is not enough insurance—especially if this damage happens early in the tenancy. For this reason, it makes perfect sense from a landlord's perspective to charge both extra rent and extra security deposit for a pet.
Therefore, although tenants may believe you are double-charging them, in reality, the combination extra rent and extra security deposit is really an attempt to cover all scenarios—and rightfully so. Ultimately, it is easier financially on the tenant because most tenants will not have the extra money for a much larger security deposit, such as a full month's rent. Although this combination leaves you with a little more risk in the beginning of their tenancy, this risk is reduced with each passing month.
The one advantage about collecting extra rent is if upon departure, the tenant's pet really did very little damage, then you've made more money on that rental since the extra rent is yours to keep no matter what.
There probably isn't a good universal answer to this question although there is one universal element. That element is this: if you allow pets, especially dogs and cats, in your rental, then you need to collect some form of compensation in case they cause any damage. This can be in the form of extra rent, extra security deposit, or both. Whatever you choose, provide yourself with as much coverage as possible. (I cover the topic of pets in other articles available on my website at http://www.findthatqualitytenant.com).