As macro photographers, we spend a lot of time on our knees shooting. Sometimes the ground is hard with little stones and sticks that dig into our knees, or it may be wet and muddy. In either case, keep your knees happy by using knee pads. Once you use them you will never want to be out shooting again without them.
Just go to your local Home Depot or what ever home improvement store is near by and pick up a pair, even the cheap ones work fine. I have a pair of cheap foam pads that have velcro straps that wraps around your leg and holds in place.