I have velcro on the kneecap sewed on by a tailor. Made sure it was right below where my knee bends so if I used the armor it would actually protect my knee/upper shin since they aren't flexible.
I also hot glued velcro on both the inside and outside of the elastic straps and hand sewed a piece velcro on my outer knee to make sure it stays straight and didn't droop from the weight of the metal darts.
I taped over the darts inside the knee piece with some clear packaging tape to be able to put velcro on the inside as well on a flat surface.
If you need photos of this let me know. It's never failed me in my 5 troops!