@Stuart Somewhat of a manual process - not sure if netsuite has anything native to do this- but you could create a item account linked to the liability deposit account. When you invoice the funds would show up in that liability account and AR (Debit AR and Credit Deposit account) - in this method you would have to reconcile the billable hours every month from the amount that is sitting in the liability amount- Basically Debit the Deposit account and Credit Revenue - what ever is remaining in the liability account is what how much of the deposit is remaining for that particular client.