just though i'd add my experience
Zak is a working cocker and was undocked when we bought him. Although we don't work him his natural instincts are very strong and he loves nothing more than to flush pheasants, chase rabbits etc through any sort of undergrowth.
When he was about two he started to damage the end of his tail quite badly.It really is awful to see your boy with a bleeding tail. He obviously didn't notice the pain until afterwards.
After several visits to the vets we were told that he would have to have part of his tail amputated. It was a very traumatic time for Zak and for us. He was on lead walks for a long time to let the amputation site heal properly and the hair to grow back.His tail is now just a bit shorter than a working dock
Thankfully he made a full recovery and 3 years later he chases to his hearts content and has never had any more damage
Strider is also a working cocker. He has a working dock, goes in exactly the same undergrowth as Zak, in fact probably even thicker stuff and has never had any tail damage.
sue,zak and strider