Sounds like my Apache, he's going to be 11 and has very bad arthritis. He was never a big fan of "the rake" which is the only thing that will get his thick undercoat. I can do his top line, chest and belly but as soon as I go near his hind quarters that's it. At his age I don't push him.
Apache - Shiloh Shepherd 12/15/02
Kiya - Shiloh Shepherd 5/15/04
Lakota - WGSD 1/13/10