Good question and a very important subject! I always look at my outstanding balances, before you get into a place where a lot of money is owed I like to shut down any new calls for that client before a lot of money owing is accrued. I think important terms would be your invoice due dates, there are options in the settings where you can adjust the date an invoice is due. Jobber will also continually send emails to a customer when an invoice is outstanding which is a great feature.
And to your main point here, if its in your contract and a lien is needed to be delivered, you are within your rights to do that. I would make sure you had a lawyer look over that contract to make sure no one can pick apart your verbiage and your terms are clearly laid out.
