The Dude has minions and nihilists walking into his apartment the entire movie and kicking his ass, stealing his carpet, throwing ferrets at him, smashing his stereo. So he finally decides to do something about it. He spends about an hour hammering a stop to the floor as a brace for a chair under the knob. It looks pretty solid, probably foolproof.
Big Lebowski Door Reinforcement Procedure
I laugh harder at this scene every time I see it. It is kind of like DUMB AND DUMBER, where the first time I saw the movie I thought it was just kind of silly and juvenile ... and the tenth time I saw it, I considered it brilliant cinema.
Remember this principle when you are reinforcing your house against intruders.