I guess that depend of where you are.
Here where it is frosen it is mostly just any meat or chopped up carcasses tied to a pole or even better dug down before it freezes and then poled open at winter. so that the fox smell it but never really finish it.

One very interesting method Iv heard of but never tried would be to use grain, wheat, barley or whatever in a tube set vertically down in a pile of branches. this would not attract fox but mice which in turn gets the fox. This should increase the effect on mousecalls to.
Has anyone tried this?