There is no method to protect against destructive fantasy :-)).
If you do not believe me, let a kid alone in a room with whatever protected device (safety warning here!) for one hour.
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What power source do you plan to use?
One capacitor (tens microF) on source can help reduce spikes at the connection moment.
Diodes can protect against reverse polarity (voltage drop applies). But the same protection you can achieve by whatever non-symmetrical connector (one that can not allow, by its shape, a reversed coupling).
But an USB connector can be mounted only one way, so the risk of reverse polarity is low in my opinion.