Thank you for contacting Just Answer.
One thing you can do is sign a promissory note for the balance due, including interest, with a deadline, and then a penalty per day (or week or whatever) if the final payment is late.
The owner needs to understand that you are not a bank and that you need to pay for your labor and materials.
So, to maintain good relations, if you can afford it, I suggest that you take the $5K now and give the owner a few weeks or whatever for the other money. If you write a promissory note, it would be good for it to be secured by some type of collateral, or even a bond.
Otherwise, I agree, a Mechanics Lien is the way to go.
If that answers your question to your satisfaction, please click "accept." Thanks, Jane