This wound, I agree, does sound rather extreme.
Usually after infection (say an abscess etc) has burst, it is best to keep the wound open and ensure it drains fully before healing takes place. Most often such wounds are left open to the air, but in certain cases need to be cleansed regularly.
However in this case it sounds as if you need to keep in very close contact with your vet, and be aware of any changes, and take your dog back in ANY time you feel something is not right.
It is amazing how even deep and horrid-looking wounds do close eventually and heal. The tissues regenerate and knit together. So long as infection is not present, and the wound is cared for properly. Of course it is wise to keep that wound covered when your dog goes outside, to keep dirt off it.
One thing you have to watch for is flies. Don't let flies get at it.
I can understand the "hole" which appeared. Even a bad abscess, when it bursts, often leaves a deep and angry-looking hole in the skin, which can appear quite scary. That happened to my dog, and I was convinced that hole would never heal, but it did, very well.
I would say that if you are unsure about the care your vet is giving your dog's wound, then there is no harm at all in seeking a second opinion from a different vet. This wound does sound quite serious.
Could this have been a POSIONOUS snake or spider bite & the surrounding tissue is actually rotting away? I think your Vet needs to see this in person instead of by phone! IMO, open wounds are hard to manage.....Let us know how it going.....Good luck, Karla
P.S. I've had good luck with Manuka Honey for open wounds, but have never had access to the patches.....
I agree with Misfits4Me, it sounds like it could have been either a poisonous snake or maybe a brown recluse spider that bit your dog. Brown recluse spiders and some types of snakes have a hemotoxic venom which causes a necrosis (death) of the skin in the area surrounding the bite.
As far as the wound itself goes, however, I can tell you from personal experience that wounds that appear to be huge and impossible to close can and do heal completely given time. The trick is to keep it clean and free from infection. I have a cat whose entire left side of her chest was left open with the muscle wall exposed. She had been a pregnant stray that I took in, she had a litter of six who all died within a day or two after birth except one, who, even though he died before he was two weeks old (something had affected the whole litter, probably not the least of which was that the mom was only about 4 months old when she got pregnant), nursed almost constantly. I don't think she was producing much if any milk, so I fed the baby from a bottle but he still insisted on nursing and she, as most cats do, insisted on laying there and letting him. Anyway, the chest abcessed, it broke open, the whole left side of her chest skin was just GONE. It took about two weeks, but one day when we went to clean her, we noticed pink, healthy tissue growing. After about two more weeks, all that was left of this hideous wound was a thin pink line. In two or three more days, even THAT was gone, the hair was growing back in, and now she's the fattest, cutest little cat, spayed and healthy, without so much as a trace of her ordeal.
So keep his leg clean, follow any instructions your vet gives you, and chances are you'll be pleasantly surprised with how well your boy heals. Please keep us up to date on his progress!