I agree with David and Ken. It can be a difficult decision - especially when the customer has outstanding loans with your bank. If you don't think the customer is involved in illegal activity and your SAR is simply to report structuring, then consider "educating" your customer on the bank's reporting requirements related to CTRs. Many business owners are misinformed. Believe it or not, some CPAs tell their clients "never conduct a transaction with more than $10,000 in cash - or you will be audited!" Crazy, but true!
You might consider putting a section in your deposit agreement regarding "Cash Transactions."
When you discover legit customers structuring, have them read the information. I think a company named Bank Security, Inc. sells a brochure that you can use - someone else correct me if I have the name of the company wrong.