not to mention feeding, walking and all the other care it requires
My youngest son and his wife have two Great Danes, they do eat quite a lot. But both are lap dogs (or at least thing they are) and don't require too much exercise. They're smart and very intimidating when protecting their owner. An older couple need not fear tripping over them.
I had a St. Bernard in college, other than the drools he was a great dog. When he spoke, everyone listened - dogs and people. My last dog was a mixed breed German Shepard/ Keeshhound, she weighed 54 pounds and was the best watch dog. Her warning bark was sharp and befitting a dog much larger and more vicious.
Once I was working in the garage and a salesman came in uninvited and she scared the piss out him. She didn't bite him but bared her teeth and told him off. I told him not to run, had he done so I'm not sure how she would have reacted. When I found out what he was doing I told her he was OK and she immediately calmed down.
In that case no harm was done; some of those gun owners who post here seem to want to be able to use their gun(s) on another human being - as I noted above some seem to have very active fantasy lives. I suppose George Zimmerman had the same sort of fantasy.