how can I make sure that a 'lease option' is fully binding?

[Berl Weber]

when signing lease option contracts with a seller with a purpose to rehab and sell for a profit, how can I ensure that the seller will not back out after the rehab, or sell for someone else? after all I only have a purchase agreement, not title/ownership? and what's about insurance - what if the property gets damaged after the rehab, how can I get back my money invested in the rehab?