Place the safe where easy access to the back and sides is denied. For example, a corner location prevents access from the back and one side. Using something heavy and bulky, such as a refrigerator or washer and dryer, on the other side would hamper anyone trying to move the safe or use power tools. The more cramped the area is around the safe, the better.
Bolt the safe to the floor using the predrilled floor holes. Make sure the bolts go into either concrete or floor joists. Use a steel backing strip under the bolt head to prevent the head from being stripped through the bolt hole by a power jack. Some safes have predrilled holes in the back so they can be semipermanently attached to a wall. Bolting a safe to the wall studs will help ensure no one can move the safe without a great deal of work.
Fill the safe floor with heavy objects, which will keep its center of gravity low. Storing ammunition and other heavy material on the floor of the safe prevents it from easily tipping over onto a dolly.
Install a fire alarm directly over the safe. Any drilling or cutting that a thief would do will most likely create enough heat and smoke to set off any alarm.