to go to the dogs = to become less successful, to deteriorate
My uncle likes to repeat that the country is going to the dogs.
every dog has its day = everyone is successful or happy at some time in their life
As they say, every dog has its day, so, be patient!
the hair of the dog (that bit you) = an alcoholic drink that people drink to alleviate hangover.
It seems I had one too many last night. Need some hair of the dog.
to lead a dog’s life = to lead a miserable existence
I’m tired of leading a dog’s life.
dog-tired = extremely tired
Every day I come home dog-tired and fall asleep at once.