http://revach.net/article.php?id=1019

Section: Halacha   Category: Tshuvos
Rav Shlomo Zalman Auerbach - Hataras Nedarim: "Next Year's Promise Are Null and Void" - Does This Work?

After the three people in the group are Matir our Nedarim we tell them that we are letting them know ahead of time that any promises we make from now on are null and void in advance. Does this language excuse us in the future when we make a promise?

Rav Shlomo Zalman says that it works for any mitzva that we say we will do or any mitzva that we do three time without saying "Bli Neder".  In both these cases they obtain the status of a neder and we are obligated to perform it even if we don't explicitly make a neder.  If we explicitly say that it is Bli Neder than there is no obligation. Therefore says Rav Shlomo Zalman even our saying ahead of time that we don't want these to be considered a neder is effective.

Of course if you make a promise you must keep it no matter what. (Halichos Shlomo)