Yeah, that would be kinda bad if they kicked in the door and coins went flying everywhere. I also hope it wouldn't sound like a piggy bank being shaken every-time you opened the front door. The neighbors would think you are quite a handyman working on the door every-other day...
i don't hide my coins. i place them on tables, ect. right out in the open. and i leave my doors unlocked.
Get yourself a cat box and some cat litter and hide your coins in the bottom place some plastic over them then the litter on top. This will only work well if you don't actually have a cat though lol.
Don't forget to throw some fake poop in the litter.... so that the thieves that come looking for your coins will think you have scaredy cats that hide from strangers.
Further up non_cents made the point that burglars don't spend a lot of time hanging around and looking into anything -- they pretty much grab and run. With that in mind you can keep anything that you don't want the cops or the robbers to find in the attic or the crawl space, neither of them are going up/down there. I was burgled a couple of years ago: they kicked in the front door in the middle of the afternoon (broad daylight) while I was at a movie. The alarm went off and the dog freaked out and apparently they high tailed it without even entering the house. The alarm company called the cops, who were on the scene with a response time of less than 5 minutes to catch my dog and cat and get them back in the house. The burglars didn't go through anything, even laptops and tablets that were sitting right by the door that they kicked in. The cops caught my animals and then went through the house and pulled out the firearms they found in the closets, etc., I assume checking their legality. No one went into the attic though. So get an alarm, get a dog, and hide anything valuable/illegal/embarrassing in the attic or crawlspace.
When I had a burglary a few years back, the bad guys actually kicked in my steel exterior door, permanently deforming it about 3 inches (kicked the deadbolt right through the framing!). My daughter came home and found the door laying on the floor. I suspect they'd discover your coins under those circumstances.
I was only joking, anyways...... Personally, I doubt if there every situation can be covered no matter where you "hide" your valuables. A SDB is probably the best thing for truly valuable items. But only because it is less likely to be 'burglarized' than a home. Accidents and Natural Disasters do occur that take out those as well. It's all a matter of what you feel is the 'safest way' to attempt to preserve your collectibles and/or other valuables.
I bought a 45 gun safe from the sporting goods store that has a humidifier in it. It works well but is full now so i am about to buy another. You can watch for coupons and when they go on sale and you can get one for 1200 or so.
The best thing you can do is keep the fact that you collect coins a secret from everybody. People talk to people who talk to people (both in & outside of your family). When a bad guy goes out to rob a house, if they don't know you are a coin collector, then your house will not be specifically targeted. The other obvious good comments have already been made. Get a SDB, insurance, and alarm system. Primarily, keep the fact that you are a collector top secret. Specifically instruct your spouse & immediate family to NEVER discuss that you are a collector. Never discuss your security system & where you hide you coins in an open forum. Like scottishmoney said, I could tell you but then I'd have to kill you. Hiding your valuables under a cat box has been discussed muchly. Sooner or later every burglar is going to be kicking over cat boxes. In general, burglars don't bother with the kids rooms. My kid has moved away so I don't have a kid’s room any more. My home was randomly selected for a burglary a couple years ago. I posted about it here. The guy spent some period of time in my house (seconds) and he was subsequently arrested & convicted. I forget the exact sentence. It was something like 10-16 years without parole because of his career criminal activity. NY gets him after he finishes his current sentence.