Sold 34 acres on my own paper, and the partial release clause almost killed it

The mechanism you used is the standard answer to a subordination demand, and the number that decides whether it holds up is the release price relative to the actual value of what leaves your lien. At 6,200 per acre against a 4,940 allocated average you are collecting a 25% premium, so on paper your remaining collateral coverage improves with each release. That only holds if the allocated per-acre values are honest. Frontage acres in most raw land deals carry a large multiple of the interior, so if the first eight acres are worth 9,000 and the back slope is worth 3,000, a flat 6,200 release price strips value faster than it pays down principal. The frontage-in sequence protects you against cherry-picking within the parcel and does nothing about that pricing mismatch.

Worth running before he exercises anything: for each step in your release schedule, what balance remains and what would the remaining acreage sell for in a distressed sale. If any row shows remaining balance above remaining collateral value, the release price is too low for that step. Some sellers fix this with a tiered price by zone rather than a flat number, or by requiring the balance to drop below a stated fraction of appraised remaining value before further releases.

On the other side, partial release recording practice and the form of the release instrument vary by state, and so does whether transfer tax applies to each release, so confirm both with your title company and attorney in writing rather than assuming the first one sets the pattern.

Your income falling as he releases acres is the design working. If steady payment size matters to you more than principal recovery, the lever is a prepayment premium or a floor on payments, and that's a term you would have had to price at the start.