Your problem is going to be getting sure DRT shots while saving fur on both fox and coyotes. Unless you have some giant foxes or some midget coyotes, they are too different in size for one round/load to be ideal for both.
The hornet will work on coyotes at shorter ranges and with proper shot placement, but you either wind up not taking shots that you would not hesitate to take with a larger cartridge, or you will have a greater number of wounded runners.
The .223 will work on foxes, but you will have a greater number of ruined pelts than with a hornet.
As with most things, a compromise means something that works more or less in a number of circumstances, but isn't ideal for any. You just have to decide which side of the compromise is better for your needs, circumstances, and abilities.