Watch for infection where the tail is swollen - if it is warmer to touch than the surrounding skin then you need antibiotics. Are you sure the bulge is not made up of wool? It's years since we last docked a tail and I don't remember any problems.
Getting those rocks off the tail can be difficult. My OH has been seen using daggers or foot shears to cut through the rock itself, snipping off pieces until it's mostly gone. Or sometimes you can crush it in your hand, whilst avoiding the tail. We have tried vaseline to prevent the rocks from building up again but without much success. They are a particular problem with Soays of all ages - tiny tail but just as much s#!*
Our dogs are in seventh heaven if they get one of those lovely lumps of solid poop to munch on