Hello ra-property,
I'm happy to give my suggestion; though realistically, you'd NEED to get an accountant to tell you the correct method to record this within accounting, and then we can translate this over.
You may be able to just record a deposit straight to the tenants debtor account; or you may need to record the value of the security deposit under a different asset account within your balance sheet.
Do you know which method you are expected to follow, or can you tell me a bit more about how your accounts professional expects this to be recorded within your accounting system?