grant/revoke rights

Can someone direct me as to why the rights that I specify for a given table
doesn't take affect? I revoked all rights to the "Public" and the postgres
default id "nobody" can still do inserts, deletes, updates, etc.

I do a "\z" on the table and it shows no rights, but still allows anyone w/
a valid
postgres id to wipe out any row they wish. I've even tried to manually
revoke the rights from "nobody" and it still doesn't work. Are there
setting some where that "turns on" the specified privileges intiated by the
revoke/grant commands?

Thanks in advance.....