What are some good, non sliding volleyball knee pads?

I have the mizuno VS-1 volleyball knee pads, and they're comfortable and all but the top part always tucks behind the pad whenever i bend my knees and it's SO annoying! also if im at practice and were doing exercises where I have to bend our knees they start sliding down under my knee and its super annoying. And im 100% sure they fit, i got a size Medium and a Large is way too big and a small is way too small. So can anyone help me find a really good pair under $30? basically one that doesn't slide too much, they don't have to be super padded, but they don't have to be super light either. I just want a pair that won't slide whenever i bend my legs. Thanks!