Im sure one of the trough style feeders would reduce what goes on the ground. Several use the timed trough feeders with good results and I would bet you can set them to be free choice also if you wanted.
I use to have Coons, Squirrels and Birds get into my protein feeders. I changed to a 20% L&E protein feed and now nothing but deer eat it. Not sure what's in the L&E that the varmints and birds don't like but it started as soon as I started using L&E.