[MSAccessProfessionals] Add lock key to records..

I would like to add a lock to records once an invoice is sent out.. to prevent accidental changes.  

My first thought is to add a field (Lock) to each record and then add a before update procedure on each field, many of the fields also have after update procedures, 

Can I use both Before and After update procedures, 

Is there a better way to lock down records. 

Take care,

Mike the Plumber

Sac City Plumbing

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