Defence in Depth: A 'layered' strategy can repel cold attackers

Yes, a vest, cardigan and an overcoat

The principle of Defence in Depth ("DiD"), says OWASP, is that "layered security mechanisms increase security of the system as a whole". That is, if one layer of protection is breached, there's still the opportunity for the attack to be fended off by one or more of the other layers. If anyone's ever drawn something that looks like an onion on the whiteboard - a load of concentric layers with your infrastructure in the middle - that's the concept we're looking at. It's actually a military term that's been adopted by security types in the IT industry who want to be tank commanders when they grow up."