I recently had the pleasure of breaking into my own house after arriving at work and discovering that I only had my car keys on me - it was an eye-opening exercise. I was fortunate that I had not engaged the deadbolt on the door between the house and the garage and happened to have my garage door opener so I had access to a number of tools. My first thought was to see if I could spread the door with some of the Jorgensen clamps I had onhand, but those were not reversible. I then improvised a spreader with some scrap lumber. Despite successfully spreading the frame somewhat, there was not sufficient clearance for the latch to release (nor was there room to try to manually creep it forward). I foolishly tried to use the door handle itself as a pry point and only succeeded in bending the stem by about 15 degrees. At this point there was little point in subtlety so I grabbed the sledgehammer and about 4 blows later the handle failed spectacularly, allowing me to rotate the latch and open the door. The entire process took about 20 minutes and generated no attention from the neighbors (I did this in the garage facing the street with the door open) ... a determined thief could have gotten in within 2 minutes' of gaining access to the garage (and they would need the opener and/or take the time to break down the garage door itself).
Many years ago, a break-in at the family home was foiled only by the stupidity of the thieves. A neighbor across the alley watched a utility/service-looking truck pull into our driveway and thought little of it - even when one of the occupants stood in the driveway and looked around in a vaguely uncomfortable fashion. The neighbor immediately realized something was very wrong when the other occupant jumped over the fence into their backyard a few minutes later, only to realize they were being observed. Both would-be thieves then vanished in short order. We all concluded that the neighbors' lower 6' perimeter fence was the sole factor in preventing that incident.
Fortified structures for security against intrusion is about deterrence and physical security. Deterrence factors include security lighting, alarms, and lack of visual/sound cover. Physical security include tough doors, security films on windows, pick-resistant locks, reinforced door frames/walls, etc. Both can be implemented on existing structures with varying degrees of success.
Hardened structures capable of surviving disasters are a somewhat different discussion. There is only so much that can be done with existing structures to deal with large-scale forces such as hurricane/tornado winds, earthquakes, or floods.
Security fortification features seem a good deal easier to implement on existing structures than disaster hardening. At some point you need to look at cost-effectiveness and assess how realistic your plans are - lest the producers of Preppers ask you to appear on their program so they can make you look like a nut and their experts can do the analysis on your plans after-the-fact that you should have conducted earlier.
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