Steve's post brought to mind something that happened to a cat belonging to
one of my colleagues at work a couple of years ago.  The symptoms sound
identical.  It was established that the cat had been knocked down by a car,
and dragged (his claws were damaged where he tried to hold on to the road)
and caused a sort of dislocation of a vertebrae near the tail.  This cat had
no control of his tail - but I can't remember about his legs, sorry.  One of
the worst things was that he was unable to open his bladder himself, and it
had to be done manually by the vet.
My colleague (who had two children distraught by the accident) decided she'd
nurse him and see what happened, just so he had every chance. She was told
to confine him in a small space, so I lent her one of my dog travel crates.
The main problem was the bladder, he just could not empty it on his own and
had to be taken to the vet every day to have it done (and his fluid intake
reduced temporarily.)
But the good news is, eventually he recovered, he had toileting problems
(incontinent of urine for ages) but eventually that cleared up too and now
he is as right as rain.
I hope this will happen for Rocky, but I'm afraid it will be a long haul for
you both. Prayers that this will happen, that the vet agrees he has a
chance, and you are able to nurse him.
I'm so sorry about this, Steve.  It was what I was afraid of when Kitty FC
went missing, but we were lucky.

{{{more hugs}}}
Tweed