There is the “parcel has avie protection” option. This option when is activated, makes the avatars invisible to anyone who is not in your property! Even if someone steps behind your borderline, they will not be able to see you, or anyone else in the parcel!
That selection can be found if you open “about land / options (it's right above the snapshot: see and chat with residents on this parcel”, the selection box must be deactivated!
As to your lands sound settings, to prevent hearing any sounds from the neighboring lands, (such as voice, chat or streams), you should open the “about land” and select the tab “audio / sound” and make sure that those two options are activated:
Restrict gesture and object sounds to this parcel
Restrict Voice to this parcel