Joe, I certainly know how you feel. My 12 1/2 yr old German Sherherd is having a difficult time getting around, and I dread the day he leaves us, as my children grew up with him, playing in the open front yard, never had him tied up, he'd 'shepherd' the children and keep them in the yard.
My previous Shepherd was my police K-9 partner and he saved me from injury on more than one occasion by reacting to a threat much before it registered with me and I could react. They really do have a sixth sense and seem to know what's coming long before we do. When I had to put him down, i thought I'd have a heart attack for several weeks thereafter.
Also, my father-in-law did have a heart attack after putting down his Malamute, he was driving to work, and only approx. 3 weeks out of the year did he have a car with a police radio in it, and this was one of those weeks, so he was able to call for help, and help happened to be really close by, and he was rushed into quadruple bypass surgery.
Reading so many posts here about how sad it is to deal with the loss, I'd remind everyone that we all did give our friends probably the best care and the best life a dog (or cat) could ever hope to have, and I'd like to think they felt as happy about having known us as we do about them.
One other thing- somewhere a few years back I read of a suggestion to us photo folk, and I've been doing it for a few years now. When you are going to remove a film from your camera to get it developed before all the frames are used up, use the remaining shots on your pet, because many times they leave us and we wished we had taken more photos.