<p>Large institutional investors collectively spend tens of billions of dollars annually on portfolio management, custody, compliance, and advisory services. Yet the same institutions spend almost nothing systematically identifying, evaluating, and enforcing the legal and contractual rights that accompany those positions.&nbsp;</p> <p>&nbsp;</p> <p>This article terms that gap the “mortgage on ownership”: institutions pay the full recurring cost of holding title while voluntarily surrendering the conduct that ownership requires. Drawing on SEC enforcement records, securities class action recovery data, and the structural architecture of limited partnership agreements, the article documents three compounding failures—the claims recovery gap, the fee calibration problem, and the contractual gap—and argues that each is best understood as a form of institutional adverse possession: a structural recalibration through which counterparties take effective governance possession of terrain that institutional owners have abandoned. Using the English Party Wall etc. Act 1996 (England and Wales) as a model for proceduralized rights enforcement, the article proposes concrete reforms to limited partnership agreements, investment management agreements, and side letters that would normalize rights enforcement as a fiduciary obligation rather than a relational risk. The central claim is that ownership is established not by scale or title, but by conduct—and that what is not defended is not owned.</p>