I know these are generally not a good idea, but hear me out.....

Before my old HVAC system and ducts were changed out, I added some supply filters on the vent registers as a temporary measure. I did this because after having to CUT an access into the return ductwork to clean the coil, I could see the whole system was filthy. We had significant dust and mold on both sides of the coil and the ducts leading off the plenum. When I removed the vent registers to snake the vacuum down into the duct, all kinds of junk came up.

With 4 cats and 2 dogs, I would like to put some kind of mesh or screen over the floor vents to prevent large debris like dry dog or cat food from dropping into the ducts. Obviously, I don't want anything that will restrict airflow too much. I used to use the WEB vent register filters, but that was on my old system, which had one foot in the grave anyhow. My new system is a Trane with variable speed fan, solid metal duct and 5" MERV 10 media filter. Air flow seems great right now.

Does anyone have any input or ideas on what might work?