Locking? When does the detent thingy 'lock' anything? The very shallow texture on the barrel nut causes a small rattling noise when you tighten or loosen the barrel nut, but at least on mine, there is no real resistance. And the barrel nut working loose is one of the most common complaints about the ASR. That little clicky thing just doesn't do anything. That's of course why I made a spring plunger with a tempered steel rod dropping into a matching hollow in the barrel nut. It was a tricky bit of machining, both making the device and aligning it correctly, but it works very well. That barrel nut is NOT moving once the rod clicks into place. Not until I lift the little knob to allow loosening when I'm taking it down.
I suppose you could also very carefully carve the little grooves further up toward the threads. That would be tricky, and useless, as all it might do is extend the clicking a bit further, still without locking the nut.
If you're not set up to make a proper barrel locking mechanism I'd recommend either a drop of blue Loc-tite on the threads, but not too much, just enough to prevent a range trip from loosening it while you shoot... or constantly checking the barrel nut to make sure it's tight.