> Short circuit proof, reverse polarity proof and the like.

A common cause of problems is power supply, particularly wall
warts or battery eliminators. My normal practice is to put a full
bridge on the power input. That way the customer can use any
voltage between around 8 and 25VDC any polarity (assuming
5V circuit and a little margin for regulator heating) or around 6 to
20VAC. Bearing in mind the recent discussion about the wayward
specs of wall warts it's cheap insurance, as well as giving the end
user some choice and protection if the original wall wart goes missing
or whatever and they buy a new one

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