i have a rott/shepherd mix who is approaching 11 years old. his rear end is quickly declining. the vet says it's some combination of arthritis, hip dysplasia, and degenerative mylopathy (a shepherd thing?). he can still get up on his own when he really wants (esp if food is involved) and is generally still in great spirits. but it is getting worse fairly quickly. for example, he will at times poop where he lays instead of going outside (though he still waits till outside to pee). so how do i know if his quality of life has declined enough to think about ending his troubles?