Just beat some eggs up and put em in a jar with a lid on (don't over tighten it) and bury the Jar up to the Lid - leave it about a mth or so, what should happen is it should turn into a creamy/oily mix, just do your usual dirt hole set and put a small amount on a stick and put that in the whole, foxes love it.
P.S. make sure you wear gloves when setting the traps (use a pair of gardening type gloves) and also use a pair of those disposable gloves when handling the scent as you don't want to get scent on your traps or the little bastards will dig em up!!
Use good stakes to keep the trap in place (12" Reo with a nut welded on top is a good cheap way to go) and use 2 stakes if you think dogs are a possibility.
There's heap of vids on Youtube so have a good look and you will soon learn what the go is.
Have a look at a few vids that my mate Max has made on trapping foxes.
https://www.youtube.com/watch?v=5ubg4USLUfU