Sorry, I have nothing much to offer in the way of collapsible walking sticks for defense, except that personally I would never use one.
What I did make once, just as kind of an experiment for ocean kayaking, was a wooden pole with a long spike driven lengthwise into one end and the head of the nail ground off and then sharpened. It extended out the end of the pole about 6 inches. The spike itself was covered by a section of the pole that I had previously cut off to make the pole the length I wanted, and then I had drilled a hole slightly smaller in diameter lengthwise down through that section so that it would friction fit fairly tightly over the spike. This made the pole look pretty much like just a regular wooden pole except for a thin joint between the spike cover and the rest of the pole. If I wanted the spike exposed, all I had to do was slide the wooden section off the spike end.
This pole somehow got lost during a garage remodel, and I'm thinking of making another one. This "spear" wasn't nearly as light as the hard-drawn aluminum tubing with rubber cane tips on both ends that I typically use as a hiking staff, but that was no big deal because it was bungied to the top of my sea kayak. I'd definitely like to have a spiked hiking staff tho so will look into finding a narrower hardwood dowel soon.
BTW, the nail I used for the original spike was a very long galvanized nail used for fastening rain gutters on the eaves of a house. That's the longest "nail" I have ever run across and hopefully can locate a couple more of those.