I always wore external knee pads for tele skiing and started wearing them for fishing about 10 years ago. Boy, the external pads have done a great job protecting my knees
and my waders when bushwhacking, getting low for stealth, and kneeling to release fish.
Contractor knee pads always seem to slip
badly; especially when worn over waders. When I got into Tenkara fishing 4 years ago I noticed many Japanese T-anglers were wearing these "wader gaiters".
Gaiters to wear over breathable wader. With them on, you will feel decreased water drag while wading…
www.tenkaraya.com
That $68 price is a good deal! The last time I looked they were being sold here in the US for about $100. Quite a few US T-anglers buy MIJ gear from Tenkara-Ya and say good things about the gear, the purchase process, the staff, and surprisingly fast shipping.
But that $100 price got me reading about less expensive alternatives. I tried these.
Equip your department with top-rated Knee And Shin Guards trusted by law enforcement professionals. Quality gear, competitive pricing, and expert support.
danasafetysupply.com
They stay in place well and don't bunch up over nylon waders but were overkill on the protection side for fishing. As a result they are bulky and rather heavy
that makes it feel like they restrict movement a little. I still have them but loan them out to my son or friends on trips.
Then I read about these from a company in the UK. I got mine for $45 shipped and they arrived in 5 days!
https://www.tenkaratalk.com/2016/11/things-that-go-bump-on-the-stream/
but they no longer offer them

.
Made specifically as a "wader gaiter" they are nearly flawless. They're lightweight, stay put, do not restrict movement, and provide ample protection for fishing. They could be a bit longer like the *"Little Presents"* but paired with neoprene gravel guards provide great protection for fishing from the knees to the top of my boots. Love them!
I haven't looked real close since I got the Esoteric guards but soccer - dirt bike knee-shin guards
might also work. The tactical knee shin guards without a hard outer shell might be better though.