I use the mesh too.. I framed out 2 mesh covers using window screen frame. I was going to use diffuser too but i was afraid that would hurt the fish more if they jumped and hit something rigid.
They just sorta bounce off the mesh lol.
Not one fish lost! (due to carpet surfing that is)
As far as the cats.. Mine stays far away after i splashed him with tank water one day, but some cats might not be so easily deterred.
