you have my deepest sympathys about Coal.
having owned a vet hospital for 7 years, and being the worlds biggest softy for dogs, cats, horses, and donkeys (don't like people much), i have had to deal with this more than once. it has been my experience that the time you buy with the chemo, etc is not quality time. i have always told the vets that if they can give me a "real course of action", like thyroid meds, etc. i will follow the course, other wise its burgers and bed. one day you and Coal will know, "todays the day" and you and him can go on one last walk. be happy for all the great times that you had, and fill your mind with the memories. know that the decision that you are making is the most humane one for him.
i have loved all the animals that i have gotten to share my life with, and each one has been so special. and have lost some of them over time. i miss them all, and look forward to getting to share great times with others in my life.
my life now consists of 2 wild horses, 2 wild donkeys, 2 adopted pit bull crosses, an adopted beagle, and a a big fat cat. my pit mastiff cross is getting old, i have to lift him on and off the bed, into the truck, etc. but he is still having good days and he has some strange lumps, but i know one day........
all the best thoughts
dan and the family