We made a very bad choice in selecting the company to install our pool...
This company sub contracted almost all the work and as such, we had numerous suspicious (in my opinion) looking characters working around my property. I could just imagine one or more of these characters returning with the idea of robbery...
At that time, my big dog was a German Shepherd - Golden Retriever - Wolf hybrid, who is the first image I posted on this thread. She was quite large and weighed about 85-pounds (~38.5 kilos). However she was a very gentle and well trained dog but was not happy with anyone intruding on our property unless I introduced them to her. I would walk my dog around the construction site several times each working day to show her off to the crews working. She did not growl or show any aggressive behavior but, it was plain from her body language that she did not like having these characters on our property. Result: with the dog - no theft. Without the dog, who knows?
One time I had a disreputable guy come by collecting for some bogus charity. My Maltese barked at him. He laughed and said "Them are cute dogs but they wouldn't scare away no robber!" Right then my wolf who thought he was a danger to her little dog friends charged up and hit the fence with her full weight with her jaws open. The little Maltese wouldn't scare away a robber. However, they were just my early warning system - the wolf hybrid was my strike capability...
Before we began totally rescuing dogs, we would breed and show Maltese. Maltese puppies are very expensive and readily sold, thus they are are pilferable. Whenever we had prospective buyers come by to see our puppies, I would also introduce them to my wolf-hybrid. That was just to let everyone know what would await them if they ever returned to break into my home.
Regarding guns, I don't have anything personally against firearms as a deterrent to theft. However, I don't believe that a gun is a panacea against theft. Guns themselves are items that thieves aim at. As far as having them in a gun safe (required in some venues). You might as well store a feather pillow in that safe for all the protection that a gun in a safe affords. But, if you are not expecting to use the gun as a self defense weapon, a gun safe is probably the best way to store it (and is required in some venues).
I don't have a need for a gun safe. However, I do have a fireproof (fire-resistant) safe in which I keep many of my valuable and non-replaceable items. This safe is secured to the wall behind it. I keep our passports, insurance documentation (copies are kept off-site), personal items such as a copy of my military service record, our birth certificates, vehicle titles, home mortgage documentation and other valuable items as well as a supply of ready cash (in case the ATM's are not working due to an earthquake or some other disaster).
Additionally, I strongly suspect that most persons would have a hard time killing someone, even an intruder. Unless, you are willing to kill an intruder with your gun, you might as well revert to the feather pillow as a defense weapon. Using a gun to "scare off" an intruder is an absolutely stupid idea and will, most likely result in the gun being taken from you and perhaps used on you!
I will not even get into the various laws in different locations which make owning and using a gun very difficult and often totally illegal. I also would never carry a gun outside my home for defense. The laws regarding shooting in self defense outside of one's home are often quite ambiguous. However, in most jurisdictions within the USA, shooting an intruder within your home (especially at night) a bit less ambiguous..
But a dog, combined with a security system is probably the best choice in preventing robbery/intrusion. Actually, even the signs announcing that this premises is protected by the XYZ Security Company can be a deterrent, whether or not the security contract is in effect. I once had signs on my gates with a picture of a guard dog and a notation that read, "I can make it to the fence in 3.5 seconds, can you?"