For fox, location of the set is important. Set where a dirt road enters a field, where two different crops change or where a drainage ditch runs along a field. Remember the wind. The back of the hole should be facing the wind. So the wind blows the scent over the trap.
Most animals approach a trap set from the downwind side.
That is why it is vital for you to pay attention to the wind. Legholds can also be used on trail sets. Where you see trails entering the field from the woods is a good place. Follow the trail for a short distance. You are looking for a narrowed down spot.