Several years ago, after returning from my first Wyoming antelope hunt with numerous cactus splinters stuck in my knees (amongst other places), my wife gave me a Christmas present containing 2 pair of Under Armor basketball pants with built-in knee pads. They work really well. The pads stay in place and supply more than ample protection from both rocks and cactus. They are slightly compressing, but allow light weight or heavy weight hunting pants to slip over them pretty easily. (No fly however, so that's a work-around.) Otherwise, they do exactly what I was hoping for.