"Preventing" works best, I believe, with savings accounts, where the likelihood of dealing with a third party is remote.
Think of the ramifications of using "prevention" with a money market account with checks. A payee approaches a teller to cash a check issued by one of your customers. Your teller taps the transaction info into the terminal, gets an alert, and tells the third-party payee, "I'm sorry, Mr. Jones. Mr. Burnett has already written too many checks on this account this month. We can't cash this for you until next month."
Monitoring is the only practical choice for an account that allows third-party payments.
_________________________
John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8