One thing you've got going for you is the fact that your land lord thinks you're a great tenant. When I was in college, I had an apartment where pets weren't technically allowed, but I kept my cocker there anyway. After a year or so, I knew my landlord knew about her, but he also really liked me because I kept the place clean, always kept the yard nice, and always paid rent on time, so he never said a word about my dog. I even came home one day and found him laying on his stomach in my back yard trying to coax my dog over with a treat so he could pet her.
She hates men, by the way, so he tried really really hard to make friends with her.
Yours might not be the same way, but if he recognizes the fact that you're a great tenant, he might be able to overlook the dog.
