I was thinking of switching to demands feeders next year but I'm concerned that they will aid in the transmission of disease among the deer.

If you hang the feeders high enough varmits can't do much with them. But I did have one where some varmit gnawed a hole in the top of a plastic barrell feeder.

The on in the link is head high. Notice the cameratook a shot just when the feeder timer went off...

http://www.racksnspurs.com/images/04101711.jpg