Do you all lock your bags? (I would have thought most people do this) If not...
Try locking your zipper pulls together with a TSA approved combo lock. You can lock any two zippers together with a combo lock but it's probably better to use zippers made for this purpose. Many companies make luggage where you can lock the zippers (like Eagle Creek duffels for example).
In the past I have also used those Army Surplus bags (forget what they're called) where they lock on the top. I put my small, expensive stuff on the bottom of the bag. Better yet, put the knives in socks stuffed in a coat in the bottom of the bag as BULL4242 suggests (maybe further stuff the coat in something else just to make it a PITA for the would be thief). Those things can haul tons of gear. Plus you look "down market".
Maybe those Samsonite suitcases are more secure but I have no idea what their products are these days (too expensive for me).
No matter what you can't lock the bags away from TSA but I think locks do help from prevent theft from someone else (like baggage handlers for example if it were sitting somewhere).
Locking a zipper is not super secure but I can't think of a reason NOT to do it. You can also lock your baggage while out of your hotel room or when the bags are with the reception.
I did lose a Sebenza once while travelling but it was at a bar after arriving at my destination. It must of fell out of my pocket but who knows...

I still think about that (thinking about it is worse than the actual loss). The cerveza was too cheap and some local probably has no idea what a great knife he now has. So yeah drinking while carrying expensive stuff is not a good idea. Now I travel with a much cheaper Spyderco Tenacious. Confiscated, lost, stolen or sometimes given away to a friendly local it's easier to part with. I don't know if I could travel with a 500$ knife again.