I have two teens and I like to say that they live in an antique arena. This is a large flat place, with high walls.
In normal words it means that they have a lot of freedom and I am not particularly bitchy about that. I tell them they have to go to bed but I do not care too much if they do when on vacation. One day I will get mad and force them to do that, and they know what they did wrong and that this is the"punition". They usually come, beg a bit and I let go.
So they know that there is a lot of vagueness about the "rules" within this area, which they make use of. Also the fact that they have two parents and when they get a "no" from one, they may get a "yes" from the other (and the first one would not care)
Then come the walls. The walls are rigid and extremely strong. They know that they must not try to break them, because terrible things will happen. The most terrible thing would be a loss of trust - something they do not want. They know that we trust them and that the whole flat area above is because of that.
They also know that they can come to us with questions, to which they will always receive an answer. Some of which they will agree with, some not. There are no taboo topics (though some were complicated, when the older one asked me what a whore is (or later, what cunnillingus is) at the ripe age of 10, and the younger one (8 at that time) ran with a chair from the other room to be part of the audience...).
They also know that they can talk with us about things they will do someday - and how to do them safely. Sex is an obvious one, but also alcohol. The younger one (14) told me today that he would like to try how it feels to be drunk when he is 18. I told him that they are risks and that he must be very careful. To what he said "at home of course! with you around just in case!". I hope it will be this way but I listed the risks anyway.
Now that I think of it, we do not even exactly know what the walls are. Certainly things like theft, but they are so remote from our ethics that we do not list them.