Hello, radio_flyer. I am glad you gave notice to the rent-challenged one. Some people are going to take advantage of someone they perceive as a soft touch until they learn otherwise.

Make a sign that says rent is due in full on the first of the month. Tell them you are not the YMCA or Salvation Army. Put a lock on the refrigerator. Hide the detergent. Require a security deposit of at least one month's rent with the understanding it will be applied to making the rental space tenantable and to any rent owed upon termination of the lease provided that is legal in your jurisdiction.

Good luck.