It's all quite simple to manage. Take, for example, the double action revolver. Swing open the cylinder and snap a sturdy padlock around the top strap. The gun will not work, and an attempt to twist off the lock will wreck the gun before the lock gives way.
The above is a variant of a cop trick from the old days when cops carried revolvers. The trick was as follows. Take a pair of handcuffs, loop one of the bracelets through the gun's frame, as above. The gun is now disabled. If you also want to keep the gun from walking away, you can take the other bracelet and cuff that around a bedstead, a sturdy plumbing pipe or some other object likely to stay put.
There are many purpose-built devices meant to disable guns: trigger locks, cable locks, trigger guard inserts with padlock holes, and others. There are more besides that enclose the gun completely, such as lock boxes and safes; I think these are a bit safer; out of sight, out of mind. They also do more to discourage theft.
As to the Guardian Express article, I agree that it is senseless and tragic that a four year old managed to get his hands on an unsecured gun and fire it, killing his father. A toddler is too young to remember or to understand the Four Rules, thus cannot apply them, and thus must never handle firearms. When sensible gun handling is not sufficient safeguard, and it never can be when small children are involved, the guns must be locked up.
There is, though, a statement in the article that I find difficult to parse. The author says, "I do not own a gun for two reasons. I don't want to, and I refuse to live in fear." To the first part, very well, but I am puzzled by the second. It is not clear what the author is refusing to be afraid of. If it is fear of having a gun around, that is easily remedied and he lists the remedies: "Several methods are foolproof. There are trigger locks, gun safes and methods that will prevent a tragic accident like the one above." So I think what he means is that he courageously chooses not to defend himself against such dangers as a gun might be useful against; if that is his meaning I cannot agree. I live the less in fear for owning a gun--stored safely--and being a passable shot with it.
As a minor quibble, trigger locks are far from "foolproof." The lock must be a reasonable fit to the trigger guard of the gun or it can slip back and forth, negating the value of the lock. It is something that must be checked case by case. Not all trigger locks are good on all guns. I find it curious how often the anti-gun contingent talks about trigger locks as a panacea, when trigger locks, unless they fit properly, are less positive than other methods.
I certainly agree with Mr. Turnage that there are too many accidents related to unsafe storage of guns. Any are too many, for the problem is so easily solved. If you have disabled your gun with a properly fitting trigger lock, or a cable lock, handcuffs or something else, or have locked it up in a safe, any use of that gun by an unauthorized person is going to involve burgling your precaution, and that shifts the moral and legal burden squarely onto the one doing it.
What is to be avoided is a set of narrowly specific storage requirements enforced by law, such as they have in some countries, for one size fits all turns out to mean an impractical solution for everyone. What we need is a talking-up campaign to make sure everyone is kept aware that proper gun storage is important. Indeed, it is an essential aspect to safe and responsible gun ownership.
So I encourage you to talk it up. Though I disagree with the way he said it, Mr. Turnage and I are oddly on the same side of the issue.