Preventing users from modifying a record that's being viewed in a bound form

Hello all:

I am trying to remedy a situation where users can access the same record on a bound form.  Basically I have a form with a sub form (so a header and detail table).  On the form a user can create a new record (clicking a button).  This generates a new id and also creates a new record in the database.  Likewise, the user can use a drop down on the form to select an existing record.  What I would like is for when a user is on a record (either a newly created one or an existing on they recently selected), if another user tries to access that record, via the drop down, they will get be told that record is locked.  I tried to set the Record Locks property to edited record, but this doesn't seem to work.

Any help would be greatly appreciated.

Thanks!

Juan