Client uneasy with full payment

Hi all,

I have a client who I've worked with for many years, we have negotiated different payment terms in the past, whether it's smaller payments at key milestones or 50% up front, rest on completion, and they've even paid me in full before I've done the work which went fine.

They now want me to complete a large design project but are uneasy with giving me the large amount up front (circa 38k). In this case they have to pay for the design out of this financial year's budget.

I've provided them with my contract which states in the event of illness or death any over-payments (work I fail to complete) will be refunded.

Can anyone offer any advice on this? Is there a way to make this more...foolproof? legal? I want both myself and my client to feel secure.