A "smash and grab" is easy to defeat with a normal safe. A professional crew is nearly impossible for most of us.
The average residential burglar does not carry a forklift. He average burglar is a smash-and-grabber.
About 15 years ago, up in Portland, on a Friday evening, a bank branch manager and his head teller locked up for the weekend. The manager set the time lock on the vault door and the teller double-checked it. The manager closed and locked the vault and the teller double-checked it. The manager armed the alarms and teller double-checked. On Monday morning the manage arrived to find everything in good order... until he opened the vault and got quite a shock; it was empty! The bank's locker at the back of the vault had been cleaned out; cash, blank money order and cashier's check forms, traveler's checks, all gone. But so were the accounting records and even the employee timecards. The locker was empty. And in the front compartment of the vault, hundreds of customer safe-deposit boxes, every one of them, had been drilled open and emptied out. The method of entry was obvious; someone had cut a hole first into the building's roof and then through the reinforced concrete ceiling of this UL-listed bank vault. All alarms had been expertly bypassed. The bank branch in question is on a pad site in the middle of the parking lot of a busy stripmall. The bank in question has both a drive-up and a walk-up ATM open 24/7. And dozens of surveillance cameras caught nothing. It was a stunning robbery and it remains unsolved to this day.
My point in recounting it is that even a UL-listed bank vault can be robbed by a sufficiently-skilled and well-equipped crew. If you're facing this kind of thief, there's nothing you can do.
But what kind of thief was this? Who can cut a hole through the roof of a building in the middle of the parking lot of a busy stripmall and take everything out while all around them people are coming and going and yet remain unseen? I don't know your situation, but I don't think even with my knife collection that this kind of people will be paying me a visit any time soon.
(Who did this? IMHO professsional, governmental intelligence people did it, KGB, Mussad, maybe even CIA. For the cash? No. It was less than $10,000 as I recall; this is a small bank branch. No, it was something in one of those deposit boxes. But among the bank records taken was the deposit box signature cards. They could have looked at those records and found the box they wanted and drilled just that one. Why take everything? Answer: to cover up the one thing. And what was the one thing? A pearl necklace? An heirloom broach? No. This bank is in a working-class neighborhood. If they were after that sort of loot, they'd have cut their way into Tiffany's or Carl Greeve. Short of finding something like the Hope Diamond in one of those boxes, you couldn't cost-justify this robbery. My guess is that the one thing they were really after was information, some sort of disk or tape. Perhaps the latest microprocessor design stolen from nearby Intel. Or perhaps some Top Secret III SAR defense secrets stolen from Boeing up in Seattle? Or perhaps some nuclear Q-clearance stuff stolen from Hanford? It had to, I think, be something like that. And there's nothing like that in my safe.)
When it was built, the bank spent upwards of $100,000 on tha vault, and it got robbed badly. Don't think that of you spend $500 or $1000 or even $5000 on a gun safe that it's going to provide 100% security.
But most bank robbers.... much less most residential robbers... don't come with that kind of equipment and skill.