One time or another, you may have a landlord (or manager) who doesn't respect your right to privacy—perhaps asking (too often) to stop by your apartment just to look around. The worst are landlords and managers who use a passkey to enter your rental unit without notice when you're not at home (and there is no emergency).
Fortunately, many states have laws specifying when and how landlords may legally enter rented property. See the Tenants' Right to Privacy FAQ for details.
If you feel your landlord or manager is violating your right to privacy, start with a friendly conversation, and follow up with a note to confirm your understanding. If this doesn't work, or if your landlord doesn't follow your agreement, write a tougher letter describing your concerns. You can use the Sample Letter When Landlord Violates Tenant Privacy shown here as a template in preparing your own letter. The sample letter cites California law; you will need to edit it to reflect your state's notice requirements to enter rental property (as appropriate).
For details on tenant privacy rights and landlord's access to rental property, see Every Tenant's Legal Guide or (if you're renting in California), California Tenants' Rights.