Hi Janet,
I wouldn't get the results I do with paretic animals without chiropractic. You should try to source that for your chronic cases. It restores mobility, allowing circulation to return to the area and help make the spine more supple; takes pressure off nerve roots, such as those of the sacral plexus (which confers continence); and spreads the workload of extending and flexing the spine across all joints, and not just the few remaining ones that move.
Chronic cases like this often benefit from Wind expelling formulas that move blood out to the periphery, and increase the blood supply generally. If there is a strong sense of small bowel weakness, then Yi Yi Ren Tang (Coix Decoction) is a good choice. If the animal strikes you as being quite dry (skin, haircoat, etc.) then Du Huo Ji Sheng Tang is an option.
If you sedate BL 40 and the pulse feels more moderate (less toned), then Wind invasion is confirmed. If it was tonification that made a weak or deep pulse stronger, then a Kidney tonic is a better choice. Even something like Rehmannia Eight may work.
Lastly, for some of our old and weak Kidney deficiency dogs, we've been using the Ayurvedhic herb Ashwaganda (Withania sp.).
Hope that's some how useful.
Steve