Symmetry-enforced nodal-line semimetals are immune to perturbations that preserve the underlying symmetries. This fundamental robustness enables  investigations of fundamental phenomena and applications utilizing diverse  materials-design techniques. The drawback of symmetry-enforced nodal-line  semimetals is that the crossings of energy bands are constrained to symmetry- invariant momenta in the Brillouin zone. On the other end lies accidental nodal-line semimetals whose band crossings, not being enforced by symmetry,  are easily destroyed by perturbations. Some accidental nodal-line semimetals have, however, the advantage that their band crossings can occur in generic  locations in the Brillouin zone, and thus can be repositioned to tailor material properties. We show that lattice engineering with periodic distributions of vacancies yields a hybrid type of nodal-line semimetals which possess symmetry-enforced nodal lines and accidental nodal lines, with the latter endowed with an enhanced robustness to perturbations. Both types of nodal lines are explained by a symmetry analysis of an effective model which captures the relevant characteristics of the proposed materials and are verified by first-principles calculations of vacancy-engineered borophene and graphene polymorphs. Our findings offer an alternative path to relying on complicated compounds to design robust nodal line semimetals; one can instead remove atoms from a common monoatomic material.