How To Create A Message Box Indicating Record Is Locked?

I have done some serious searching and have discovered that many others have posted this question, but I couldn't find any satisfactory answers.

I have a FE/BE Access 2000 database in a multi-user environment. I have my default record locking set to "No Locks" (optimistic), but for unknown reasons, some records still lock. The records are viewed via a form, which is also set to "No Locks." We only have about 20 users, so it is rare that two people actually have the same record open at the same time. It seems to be that whole groups of records lock sometimes, despite the fact that I'm using optimistic record locking. Usually if you wait 15-20 minutes it is unlocked. If someone can explain this I would be overjoyed.

But, I can deal with the record locking. The problem is that users have no idea why they can't update a record and no matter how many times I tell them to wait 15 minutes they still come crying to me every time. So, I want to make a message box pop up when they try to update the record that states something like this: "The record is currently locked. Please try again in 15-20 minutes."

If someone could offer some code options and explain where it needs to go (form load, open, etc.) I would be eternally grateful.

Thank you!