A landlord cannot raise the rent on its own initiative during the term of a current lease. But a landlord also does not need to renew a lease when the lease expires. Usually, the landlord does not have a right to evict during the term of a current lease, but if your landlord is serious and threatening, then what is likely to occur is the landlord will revoke consent to have the dog, and if you do not move the dog out of the home, the landlord will claim that you are in default of the lease.
This may be a good reason to consult with an attorney.
You may consider that the landlord is looking to modify the provisions of the current lease, to account for the dog, the additional security for the dog and to increase the rent. That should go hand in glove with a longer term for the lease.
Your lease likely provides that the lease may be modified as long as both you and landlord agree to the modifications and the amendment to the lease is written and properly signed and acknowledged.
So if your landlord is looking to negotiate a written modification of the lease, and you do not feel comfortable on your own to negotiate terms that may be beneficial to you, hire an attorney to help you out.
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.
Consult your lease. Is there a provision for pets? If so, it likely specifies what fees, if any, are involved.
This answer is not legal advice. You should not act or refrain from acting based on this answer. This does not form an attorney client relationship between you and Regina Gordon, Esq. Such a relationship is only formed after you sign an engagement agreement.
As the prior posters said, the lease needs to be reviewed but an attorney to see if pets are specifically included/ excluded in the lease already and what other provisions are in the lease.
Before you do that try talking to your landlord, see why he wants to renegotiate the lease, perhaps he has to pay higher insurance. If you like living there, it is much easier to come to a compromise rather than fight and move, or stay and have a bad relationship with your landlord.