Hey, thought I'd share my nem guard I made this morning. It's really simple to make.
First, pick up some crochet gridding, and cut the length to the circumference of the powerhead. Then cut it to how much you think you would need to protect the pump from wandering nems.
Then you sand the ends of the gridding on both sides to make the glue able to stick to the plastic
Glue the rough plastic and bend the other side over to glue it down
When you align both sides, put it in a vice/clamp
Get some flexible rubber tubing and cut it down one half down the middle with a razor blade
Last, cut 3 3/4" segments out and put then on the edge of the grid
Here's what it looks like when it's on a pump:
Hope this helps some people out so you don't have to worry about a runaway nem or changing a sponge.