There is a clip out there, not sure if it's the one you have been discussing, but I use them and they're great!

They are called 'Tough Top' and are basically L shaped with a slight curve and lips on each end. The lips go between the screen and metal edge of the top and then under the plastic rim around the tank. They hold VERY tightly...I used two (one front one back on opposite ends) and adult BPs couldn't push the lid up.