Provided are approaches to establish a failsafe barrier to internal bleeding from percutaneous wounds to protect a patient from failed wound closure devices or related complications due to a variety of contributing factors such as state of systemic anticoagulation, errors in surgical procedure, variability in patient anatomy, and the like. Systems include a clotting agent to encase, and thus isolate, substantially the entire wound access area from the rest of the patient and an instrument, such as an intravascular introducer sheath, inserted through a wound at an access site on a vessel, for delivering the clotting agent to the entire enveloping tissue region around the accessed area as a mold cavity to be filled with the clotting agent. With benefits of patient safety, user simplicity, and low healthcare cost driving the effort, autologous whole blood is the preferred injected agent.