impregnable/impregnate

there is nothing sexist about these terms, but they do have a sex-specific base. In situations in which their actual meaning might overcome the metaphorical use, consider for the adjective: unassailable, invulnerable, impenetrable, safe, unyielding; for the verb: permeate, saturate, infiltrate, infuse, imbue, implant; fertilize, fecundate, generate.