Greetings stringunion,
So sorry to hear about your poor roo. Dog's of all sizes are definite predators of chickens. Beaks are no match for teeth.
Yes, the wound can be pecked by the hens. But the biggest concern would be the flies. Flies will surely land on that exposed area and lay eggs, flystrike. Then the rooster will be in trouble. If the wound in not a deep puncture you can spray some Blu-Kote on the area. That will discourage pecking, flies and infection.
The best time to handle the rooster is after the sun goes down. Once it is dark the rooster will be sleepy and easier to handle. Take him off the perch, and wrap him in a bath towel to restrain him. Leave his rear end uncovered so you can examine the wound. Wear a head lamp or have someone help with a bright flashlight. Or take him into the house and care for him there. Dog bites carry a lot of bacteria into a wound. You should clean the wound with an antiseptic. Have your supplies already prepared. Use some Blu-Kote ready if the wound isn't serious. Some sterile gauze should be used for cleaning, also some povidone iodine, chlorhexidine, hydrogen peroxide or some other antiseptic to clean the wound, initially. Be gentle, yet thorough, when cleaning the area/wound. I use colloidal silver as well. It is a good antibacterial, however, a wound should always be cleaned first, then, apply the colloidal silver. Neosporin can be used, after cleaning the wound. Check the area/wound each day to make sure it is not getting infected. The first 3 days are critical. It should be healed in about 14 days.
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The rooster's self confidence will return in a couple of weeks or sooner since he has some ladies to cheer him up.
These are my thoughts on your rooster's health issue. I hope I have been helpful.
God's blessings to Mr. Loxlee for a speedy healing and long life!