Help please !!, Deal with Hard Money lender combined with Owner financing ?

Hi All:

I got a deal I must close this coming week. This is what is going on. I got an end buyer who may qualify for 75 % hard money financing, now, how could I protect myself to structure a 25% owner financing in order no to lose the deal ?, The end buyer is telling me , he just need the loan for less than 6 months. If someone can help me to structure this deal, I will so much appreciated. I got the house from the Homeowner from 128 and selling to this guy for 159 K. It is a nice fee. Please I am desperate.

Thanks inf advance to all !!