If you don't want LMB or BG going into the Catfish pond, I'd set it up so the water runs from the catfish pond to the other pond. There's the possibility of fry going downstream, or larger fish if there is a significant rain event. No amount of screens/grates will stop it.
On the flip side, if the water is high enough, fish can swim upstream too, but I'd take that chance vs. having the ponds the other way.
