Sellers Financing: More Security?

[Kyler J Sloan]

My neighbor wants to sell his house for about 630 K but it appears I only qualify for 500 K. I asked if he would be willing to carry 200 K of the deal, and he initially seemed very interested in the prospect of sellers financing -- until his attorney advised him against it. Now, he says he wants to take on little to no risk. Is there a way I can increase his confidence with additional security? 

Is there a clause I can add to ensure that ownership reverts back to him in the event of default? - Wouldn't that occur subject-to my mortgage, incurring the added risk of the due on sale clause? 

I also considered offering him a lien on a different property for added security. 

Are there better ways that I am not thinking of? 

Thanks in advance.