I had a tenant who wanted a dog.So i let him and he was an even better tenant .There are different rules in different places! For my tenant he had get permission from the neighbours before being allowed to have a dog.Not my rules but the councils .So just check you have your base covered there first with any council requirements.
And not sure if you have units or a house let .But if units be sure you don,t want a trend happening unless your prepared to be played off .
Best of luck but im also inclined to think if he is a good tenant he will have a good dog.You shouldnt have any rats anyway :)
