DEFEND (защищать, оборонять): he defended his family; he defended them from the attackers; they defended their town from/against the enemy (from/against attack); they will defend their country; he defended himself with a stick; defend yourself; defend your rights (your beliefs); he tried to defend his point (his decision); he hired a good lawyer to defend him in court; defend a case; defend a suit; the champion defended his title successfully.
PROTECT (защищать, охранять, предохранять от): parents must protect their children from bad influence (from infectious diseases); wear sunglasses to protect your eyes from the sun; this cream will protect your skin from/against sunburn; protect iron from corrosion; protect forests from fire; protect property from intruders; protect from harm (from injury, from danger, from loss, from insult; from attack, from intruders); they protect their own interests.
GUARD (охранять, сторожить; оберегать от): guard the prison (the prisoners); guard the door; guard a camp; guard a secret; guard one's reputation; parents must guard their children from bad influence (from infectious diseases); try to guard against infection (against temptation); check your spelling regularly to guard against typical mistakes; guard one's temper (one's tongue).
SAFEGUARD (охранять, предохранять, гарантировать от): she is trying to safeguard her interests (her rights, her privacy, her health); schools must safeguard the children from harm; this medicine will safeguard you against the return of the illness; new measures to safeguard the industry against/from foreign competition.
SHIELD (защищать, заслонить): she shielded her eyes from the bright light with her hand; he shielded the child with his own body; he lied to the police to shield his younger brother; he has always tried to shield her from harm (from danger, from gossip, from blame); shield from prosecution; shield from invasion; new measures to shield the companies from foreign competition.