They're a must-have for what we do. I only put my right knee down to dig so I only use one. My favorite is the roller blade brand knee pads the skaters use, very comfortable. Good Luck.
My knees have been shot for 30 years or more, and have both been operated on a couple of times. The best knee pads I've used are the gel filled pads I found at Lowe's.
I don't kneel down anymore. I dig with the Lesche T handle shovel and use a sling to hold my detector. I actually find it easier and quicker than before. I turn the sod and get the target out of the hole using the metal detector and shovel (the sling means I don't need to put the detector down). Once the target is out of the hole I use a pin pointer to isolate it from the dirt. I can refill the hole with me feet as well as I could on my knees. It took a little practice and equipment adjustments but, I wish I had started doing this years ago! Hope this helps. H Digs
Try looking into getting a pair of pants from 5.11 Tactical. Most of their pants have removable knee pads already built in. Plus they are durable as all get out and have plenty of pockets.
I'm 47 and my left knee is all jacked up from the job I do....but when I detect I think back to the person who got me interested over 35 years ago. I can't remember his name but I saw him MD-ing the school just a blcck from my house. He was on the ground digging. I went up to ask him about detecting and realized he had no legs....lost them in VN. He would pull himself along the ground as he detected.
That's what got me started....and this many years later I still love it.