Lynn, to answer your question, using Account Level Security (ALS) is the best option. Like Frank mentioned, the setup takes time but once you have it setup it is a very smooth running process.
Richard, Here is some information for setting up ALS:
To enable Account Level Security (ALS) go to the Registration window (Microsoft Dynamics GP > Tools > Setup > System > Registration).
Once you activate Account Level Security, you can’t enter, view, edit, or post any transactions in General Ledger windows that include a secured account—that is, an account to which you don’t have access.
When you use the transaction entry windows in Receivables Management, Payables Management, Sales Order Processing, Invoicing, Inventory Control, Intercompany Processing, Payroll, Purchase Order Processing, and Bank Reconciliation, you can enter, view, and edit transactions that include default distributions to secured accounts. However, account security will apply to account distributions.
You can open the distribution entry windows, but if any accounts are secured (not available to you) the account field will be blank and the message “Access denied/Account missing” will appear in the Description field. If you attempt to enter an account number that is secured, the message “You don’t have permission to create new accounts or view all accounts” will appear when you move from the field. The account and description fields will be cleared.
If you go to the System Setup PDF (By default it is located in C:\Program Files (x86)\Microsoft Dynamics\GP2013\Documentation) which talks about Organizational Structures which will be needed to use Account Level Security. You will want to refer to Part 5: Organization Structure. Chapter 24 through 27 of the PDF will go through setting up the Organizational Structure and Part 5, Chapter 28 discusses Account Level Security set up within Dynamics GP 2013.
Hope this helps. If you have any questions or concerns please let me know and I will be happy to help!