We feed ours mixed corn and layers pellets, they also graze the grass all day only being put in at night.
Regarding foxes, there are plenty round here but a good high stock fence has kept them out. Another idea is to use the electrified sheep netting around the grazing area.
If there is a persistant fox, the only real solution is to shoot it as it will breed and teach its offspring where the source of food (your geese/chickens/lambs etc.) is readily available.
I once, at a previous location, lost 20 Alysbury ducks to a recidivist fox who became quite brazen and would race in and grab a duck in front of you! I had no option but to kill it then the problem ended.
Sad to have to take a life, but unfortunately sometimes necessary for the sake of your own animals.