Your son can be evicted the same as any other tenant. Whether or not there was a formal written lease, a tenant is under the duty to keep the property clean and not destroy, damage or remove any part of the rental premises.  If a tenant breaches this duty, then they can be evicted upon proper notice. If the remain after the date to specified to leave, then the landlord need to file an "unlawful detainer" (i.e. an eviction lawsuit). Once the court issues an order to vacate, if the tenant refuses fails to leave, then a sheriff can remove them forcibly if necessary. In the meantime do not attempt any self-help measures (i.e. changing the locks, turning off the utilities, etc). If you do you can be held liable for unlawful eviction.At this point, consult with a real estate attorney that specializes in landlord-tenant cases.