I would make the security deposit at least two times the rent. That way you are not holding the bag when they don't pay the last month rent, saying the security deposit will cover it. Then you have nothing to cover any damages. Remember if the tenant stops paying rent, and you give them notice, and they don't leave, it will take a minimum (depends where you live) of 30 days for the eviction. Do you think you will collect that rent? Plus figure it will cost you at least $500 (probably more) to do an eviction.