I've placed plastic screening (large squared) on all of my overflows to prevent this very problem. It also helps with keeping food out of the overflow. One tank has it cemented in place, and requires periodic cleaning with a toothbrush. The other tanks simply have the screening looped through the overflow teeth. This gets pulled and cleaned as well.
Just make sure that the screen is slightly shorther than the tines (teeth) in your overflow. That way if something clogs, the water can still get into the return.
I like the flying hawk fish story! Glad he landed on the wet side of the tank.
-Rob