Qitzur Shulchan Arukh – 65:12
One who lends money with a house, a field, or [the borrower’s usual] place in the synagogue as collateral, and [the agreement includes that] the lender takes the profits from the collateral, it must be as a deduction [from the loan amount]. That is, he forgives him part of the obligation a fixed amount each year, that this [the profit] is the rent he is giving the borrower [for the collateral]. Even if rent would be worth more than the two agreed between themselves, it is allowed. But the lender may not rent [e.g. the house] back to the borrower himself.
There is more on the subject of collateral, many details of laws, and they really can’t be arranged without consulting a rabbi.