if you lack the combat Vet you only need to remember that random passing suspect #5 doesn't know that.

A pair of well worn, muddy army boots at the door with 2-3 fired shotgun shells (just ask someone who goes to a range if they can give you some) lying on the floor next to them will already make many would-be robbers reconsider their choice.

Criminals mostly act based on their experience and what opportunities they see: the moment they feel that the risk is higher than the reward they'll go for something easier, less risky.