I have not read this before, but I am with Jen.... We are renting out houses and trust me on this one, if we dont have every single thing in writing we are without power. The landlord can NOT change a contract without notice and without stating in the original contract that they have the right to change the conditions in the future, and then it has to state how long notice they have to leave if they opt to change those conditions.
If you do have a written contract, you have every right on your side. If only a oral agreement it is trickier, then it is month to month, so it would be harder for you to make the landlord stand up to his word, if he gave you one when you got the dogs in the first place.
Good Luck and please let us know what has happened since you first posted
Marit