I think we all know by now that knives can neither be carried on your person or in your carry-on baggage when flying by commercial carrier. Knives can be taken in your checked baggage. Some people are justifiably concerned about the security of expensive knives in checked baggage. There have been "disappearances" reported. The important thing to know is that, if you request it when you check in, you can be physically present and observe as your checked bag is inspected and then, once it is inspected, you may lock it with whatever type of lock you would like to use. You just need to request this when you check in. The ticket desk clerk will sometimes deny it because it means extra work for the clerk. Just insist. Ask for a supervisor. You can do this.
This is not a perfect solution. Any lock can be defeated and the entire bag can be stolen for opening at a more opportune time. But the same is true for Fed Ex, UPS, and USPS; losses have been reported from all of these carriers too.