This kind of ignorance makes one ill.
I cut myself once as a little kid, and never made that mistake again.
The only way a slip joint is going to bite you, is if you don't know proper knife handling techniques to start with. Even then, depending on a lock to keep you safe is an accident waiting to happen. I have witnessed this twice, or the aftermath of it.
Before I retired, I was a machinist by trade. In our shop we had this young wahoo, who didn't work there long. But he did work there long enough to amputate his right index finger by leaning on a Buck 110 to the degree that the older men in the shop gave him some harsh words over it. He snickered and said a Buck knife has a lock on the blade, unlike the old man slip joints we were carrying.
Just after lunch, there was a yell from the bench he was working at, and while leaning on the Buck, the lock disengaged, and with his weight on it, cut off his right finger at the second joint. The shop forman ran upstairs to the caffeteria while the EMT's were called, and by the time the ambulance got there the forman had the finger in a cup of ice. The got him to the local ER to stabilize, then on the John Hopkins hand clinic in Baltimore. His finger was reattached, and then he was fired for safety violations. He got injured because he was this younger generation that depends on safety devices rather than common sense. In this case, the locking blade gave him false sense of security to abuse a tool.
A couple of years ago, I needed an operation on my left thumb. I had it done at the Carrol County hospital hand clinic, and Doctor Stacy Berner was the orthopedic doctor. While waiting in the lobby for my turn to go for the outpatient surgery, there was a young guy, maybe late teens early 20's, waiting to be operated on. His right hand was bandaged up, and he was with his mother. We got to talking, and he had very seriously injured his right index finger and middle finger when a liner lock tactical knife folded up on him. He was, by his own telling, acting stupid, but he didn't hink the lock would fail. They were operating to try to get his nerve and tendon connections going again. He'd crippled himself pretty good with stupid behavior. All because he had faith in a lock held by a little piece of metal. And his father had left his mother years before, and I guess all the young man knew came from knife magazines and video games.
I was born in 1941, and growing up in the 40's and 50's, there was no locking blade knives around, with the exections of the James Dean switch blades. All the men I grew up around, ALL carried the pocket knife of the day; a two blade slip joint jackknife about 3 inches in length closed. They did everything that needed to be done with a knife, and yet cutting oneself didn't happen. I can only guess, that with a non locking pocket knife, stupid behavior didn't happen often because of the obvious result being such, that one did not have to be a rocket scientist too see it coming. If you needed a knife that you knew wouldn't fold on you, then you used a sheath knife. But then people got by with revolvers that only had 6 shots, and the simple bolt action rifle was the hunters choice.
Unfortunatly, your future father in law sounds like one of those 60's or 70's era men who grew up with little adult male supervision, but also no mentor to teach him the right way to do things. The fact that he's a so called outdoorsmen, but carries no knife says something. Your effort was well intentioned, but his type is almost a lost cause. We have some of them in our gun club, and they can be frustrating to deal with. You can't change him, so go buy him a Buck 55, and trade him the Northwoods for it. The Northwoods is too good a knife for him, he'll never appreciate it, so you may as well keep it yourself.
And next year buy him a gift card for someplace he shops.
Carl.