Great. Thanks for the additional information. I really appreciate it.
Unfortunately older dogs do tend to experience a weakening of the hindquarters with some regularity...it's more obvious in some breeds (such as German Shepherds
and Retrievers) than in others, but either way, it's hard to see your pet having trouble and not being able to do much about it.
A couple things you could try would be a Glucosamine/Chondroitin supplement to help with lubricating the joints. You can find this in the health section of any store, and you can actually just give him the human dose.
Also, you might want to talk to your vet about giving him something that lasts a little longer such as Metacam (which is much like aspirin) or Tramadol (which is like morphine) to help him feel a little more comfortable.
It's hard to know if this is simple arthritis
or if there is something more going on. Some dogs get spondylosis (which is a narrowing of the spine, which causes pressure on the cord that results in some rear end weakness), and some get osteosarcoma
cancer), both of which can present with rear end weakness. Also, there's simple muscle
wasting, which happens in a lot of older dogs.
Unfortunately, the only way to know for sure what you're dealing with is through an x-ray of her spine/pelvis area.
It sounds to me like you are a very dedicated parent, but unfortunately aging happens to all of us, and it sounds like this could be what is going on with guy. I'd ask your vet about trying some of the meds and then just do what you can to make him comfortable (I see lots of big, fluffy beds and blankets in his future!).
I hope this helps.