Yeah totally agree. The shorts don't really work in my case because the padding doesn't reach down as far as the knee. I think you need something that straps onto the right part of the leg. No problems with it sliding down as in my case it would be right above the regular batting pads.
At the moment I have been experimenting with a defrosted medication ice pack that straps round the leg. Seems to work fine, but I haven't been hit on it yet.