First off, let me say something about Emerson knives,
I trust my life to an Emerson - Ok? I cant carry a gun, because of my age, or I would. I am not always comfortable carrying large fixed blades (despite preffering a fixed blade with a blade of 4"+). So, I carry an Emerson Commander every moment I am awake. It is a utility tool and it is the knife I would go for when attacked if I had a choice. The second knife I would go for, given the choice, would be my Emerson La Griffe (fixed necker). That tells me all I ever need to know about Emerson knives - I trust them that much.
No liner problems until I had worn the liner down from use and just playing with the knife. It happens - Emerson Knives replaced the liners, sharpened it up and sent it back to me good as new.
What Greg Walker said about Emerson QC speaks VOLUMES. Greg is one of the good guys in my book, and knows of what he speaks (otherwise he wouldnt speak it me thinks).
Go Emerson. Be Happy.
Air Marshall Knife? Well if all I could carry was a Delica, I'd modify it with a Wave and a Boye-Detent (if it didnt already have one), and I'd carry that little m-f'er where I could Wave draw it with my weak hand (saving my right for my gun), and have it into Edge In reverse grip in the blink of an eye. I already carry a Delica with these mods, exactly like this (except I save my right hand for my Emerson Commander, not a gun), to be deployed like this. Comes out fast, and its ready to rock... great for Edge In. If I could, I'd have another in my right pocket too... just incase.
If I could carry any knife I wanted, I'd make it one of my own design and make, 5" double edged spear point, with a full length false edge, and a single finger groove handle, similar to a full-tang/pinned scale version of a Mad Dog handle, ground from 3/16" thick, 1" wide, D-2 steel, with textured Micarta grips. Put it in a shoulder rig perhaps, perhaps a back rig. And I'd keep my Commander in my right pocket.
The fixed blade comes out faster than a folder, already ready to rock, cuts both ways (being double edged), and pierces like an ice pick, being thin, spear-point, double edged. Its a shank, stick 'em with it, slash if you have to, to make an opening, and then stick 'em with it.
As for training? Yeah, someone like Kelly Worden, Jim Keating, Mike Janich etc. etc. I doubt my approach to knife use would be PC enough were I an Air Marshall... they'd need something tailored to a law enforcement role, more than a regular "kill 'em before they kills you" type deal.