if you only give yourself permission to enter then you are the only one that can enter
If you create a list, call it "MyCircle" and give that permission to enter along with yourself then only the names you place on that list can come in and only while you are in world. Then don't give friends or public permission to enter.
You can also create individual lists, a 'decorator' list then only the people on that list and yourself would have decorator permission, but you would have to allow them to enter also. Or a 'Sex' list where only the people on that list could have sex in your Zaby, You might allow everyone to get naked, but only allow certain people to have sex.
Of course if you want to be evil, allow them to have sex, but not get naked ;d
Please Shop responsibly and try before you buy 