Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Danny is having this issue. The antibiotic injection which was given is certainly one which I'd use for a smaller dog and is effective against infected sores or wounds. I personally haven't found products such as Chew Guard to be very effective in these cases but every vet's experience is different.
You definitely should be able to deal with this topically at home and the following are my suggestions as to what can be done:
1. Avoid use of perioxide since its use can retard healing. Instead, use over the counter Betadine or Iodine (to the color of weak tea) to gently clean the lesion twice a day.
2. Topical antibiotic ointments or creams can be used with small amounts applied after it drys.
3. A perfect product for this type of problem would be Vetericyn Spray which is available at many pet/grain stores or can be purchased online.
4. Preventing access to the area will be quite important as you might imagine so that Danny doesn't cause further damage to his skin.
I wouldn't consider this to be an ER type of situation. You should be able to deal with it at home.
And, just in case you were wondering about bandaging the tail, you can certainly try but in most cases, they fall right off as soon as the patients wags it.
I hope this helps. Deb