Putting a dog down is a miserable thing. I put my golden retriever down after having him for 5 years. He travelled with me. It was probably one of my top 10 worst days too.
The boxer I had (by virtue of living with her owner) was a great old dog. She was grown when I met her. She also had tumors that eventually killed her. The tumors pushed most of her teeth out, so we had to make her food. Chicken & Rice with some additives kept her smiling and happy.
There was an old recliner in the living room that was hers. If someone was sitting in it she would stare at them for about 10 mins, waiting for them to move. If they didn't she would sneeze on them until they got up.
She could also release the most horrible gas. The smell was terrible, but it was the burning in your eyes that made it unbearable.
She would even walk into the spare bedroom I used as an office and stand there looking at me. Then walk off. It took a few times before I realized that she didn't want to pollute the air in the living room.
clown of the dog fraternity. They do have bad gas like most short nosed deep chested dogs.