score:3
Not sure they are available in your area, but there are cylindrical covers that go over the door knob and are secured with a standard padlock. With the cover in place you can't twist the knob nor access the keyhole. The downside, it is pretty obvious when you aren't at home.
Upvote:11
It is the norm for a landlord or his/her agent to have a key to an accommodation they own or rent. Landlord/tenant laws often include an access condition to the effect that they have to give the tenant advance notice before they enter. Were you to deny them access, locking them out by whatever means, you may violate your lease agreement. Depending upon circumstances, they may have the right to break through the new lock, charge you for that, decide that you are in violation, tell you to leave.
@SpehroPefhany makes a valuable observation:
Usually there is an exception to the notice clause that in case of emergency no notice is necessary. For example, if a pipe burst in the tenants apartment and was causing damage to that and other units, the landlord should be able to enter after a bit of reasonable knocking or whatever.