Security comes in layers. As you're a renter, you are limited in your efforts to make the entire complex less attractive to burglars. What floor are you on? Is your apartment within reach of an extension ladder? Consider a stronger or extra lock on your doors. If there's a fire escape, take steps to insure a difficult entry from the fire escape.
A safe, securely bolted to the floor and/or walls is your only option. It should be heavy enough that a single burglar would not be able to muscle it out on his own. If there's extra room in the safe, add lead weight to make it even heavier.
I'm reminded of an old western movie where a stage coach company, in an effort to thwart robberies, stopped shipping gold in small ingots and, instead, cast it into one giant ingot that no one could transport on horseback.
