How do I - prevent Faceboook from sharing my post?

[Kole]

How do I prevent Facebook from sharing to all my friends what i posted on some (public) group.
I don't want my friends to know everything i post on every group or fan page etc, and in this case i had no options (owner of group controls his privacy settings). I don't want my post on some groups wall to be visible on the main Facebook wall of all my friends (including me). I blocked posts from appearing on my profile and timeline but still... the post is visible on the FIRST/MAIN page/wall (idk how to call it anymore) when you enter Facebook,

It is my post and i want it to be seen only by the people in that group and not ALL my friends.

[abraXus]

the only way to prevent it is by adding people to your restricted list