This video from the Netherlands says about itself (translated):
Feb 20. 2015
Foxes hunts alone and therefore mark their territories with scent trails. The stench scares off other foxes. A fox has several glands to spread its fragrances. Some scent glands are located near the anus and some between the toes on the front paws.
During the mating season (December to February) the scent trails suddenly smell very differently. In this period the violets gland starts working and gives the tracks a scent of violets. This gland is located at the top of the tail.
In this video you can clearly see how the fox is marking its territory. Filmed by Gerard Beekman.