Homeland Security officials are bracing for a major roadblock to President Trump’s border wall project as they begin construction on a variety of prototypes without any guarantee that funding for the actual barrier will be available by the time a final design is selected.

The agency has awarded eight six-figure contracts to companies who will set up shop in San Diego this fall to build 30-foot models of what they believe a wall along the U.S.-Mexico border should look like. Four of the vendors were tapped to build concrete-only prototypes, while the remaining four designs are expected to incorporate other materials.