Can i (like a bank) execute a mortgage on a buyers house in a deal that requires me to sell on credit?

We both agree to this; I'm selling to him alot of merchandise and he wants to pay on credit. However, so i can sleep better at night i'd like to execute a mortgage note on his house which in effect would not allow him to either sell or execute another mortgage on his house until he pays that amount. He... show more We both agree to this; I'm selling to him alot of merchandise and he wants to pay on credit. However, so i can sleep better at night i'd like to execute a mortgage note on his house which in effect would not allow him to either sell or execute another mortgage on his house until he pays that amount. He agrees to this. My question is, is there such a thing at all, and how do you go about doing it?
Update: Ok, thanks all for your answers, they were very helpful. Now, one more question, I am in NY and the other party is in Oklahoma. Do i get an Oklahoma lawyer or a NY lawyer?
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