I have a pair of these in a pair of Crye pants and I quit wearing them because they kept working their way out.  The velcro attachment wouldn't hold them in place and the edge of the inner pad would work its way out.

I heard come guys just tuck the entire pad into the pocket and don't worry about the pant fabric being behind the hard kneecap but instead shove the rim of the hard kneecap inside the kneepad pocket.  I tried this.  No luck.  They still come out.

How the hell do you guys keep the knee pads in the pants?

By being so poor that I cannot afford either item...

Could sew more velcro to the back of the pad and have some sewn inside the pocket. Other than that, I can't think of anything.
I don't have Cryes, but I mod my own pants, so I made the cut's rather tight so I don't have to worry about them coming out.

Is the pant velcro worn out? The pad velcro worn out?  Not immitation knee pads? With fresh velcro they are hard to pull out to wash. Do you have the old combat knee pads or newer Airflex knee pads?

Are these gen 1 pants? Gen 2 has a flap that you can completely cover up the knee pad. There really isn’t a great solution for the gen 1 pants. I’ve lost a ton of knee pads. A solution is to wear the black field knee pads in the combat pants. They fill the whole hole and are stiffer so they stay in better