Access to your unit is a strictly controlled thing, they need notice etc. I lived in a building, a nice one, that got lazy with this and after I told them I needed maintenance to call ahead (in writing) I had a guy show up to fix something totally unannounced, knock a few times, and then come in, while I was taking a dump.

I explained to the office in no uncertain terms that if it happened again I was going to file a landlord trespass suit and generally make the managers life hell. It never happened again and I had an otherwise amenable relationship with the landlord.

Listen you don't want to threaten anybody etc, that's stupid, but landlord relationships can become somewhat adversarial by nature. You should make sure they understand that you'll keep to yourself, but you're documenting everything, have cameras (at least let them think that you do), and that you'll shove a boot up someones ass if they take liberties.