Im ready to get down voted, but im killing my dog.

The dogs went at it again this morning. I had to taze them both to break them up. I think my wife is mad at me. We discussed it being time to put the older one (H) down and thats the plan for now. Shes getting old. Her hips obviously dont work after we get done playing, and she whimpers when she climbs the stairs. We've made having two dogs work for 2 years, and every 3 months its another vet bill because harley will start a fight she cant win. Shes getting aggressive randomly toward the other dog, and i cant help but wonder if its pain, but she keeps lashing out. My wife has already gotten hurt once, and if it happens again im going to fuckin break her neck. I will not let that dog hurt her. At this rate, im in a fucking corner and i cant handle watching this whole household hide and lick their wounds after the two of them go at it. We can take her back to the pound and theyll kill her, scared and alone because shes shown aggression toward other dogs. We can try to wait to give her up to someone on Facebook but it wont work unless they dont have a dog and are willing to take on the pain mitigation. Im lost, im tired, im scared, and its coming out as anger. I dont want to lose my dog but i wont let her continue getting worse. Its putting my wife, my other dogs and myself in danger. I love her to death. She is my first dog I got as an adult on my own. I have a thousand pictures of her just being a ham. She smiles when you scratch behind her ears. Even though her farts would kill a small child, and I'd still rather get gassed out than watch her be scared and alone at a pound. I chose an in home euthanasia doctor. Im taking the day off work and getting her a big Mac. We're going to go play ball and run around and she will never have to deal with the aches and pain later that night. She loves when I drive fast and blast EDM whole she hangs out the windows. She's just getting too old for us to handle. But she's a hard headed cattle dog so she fights through the pain all the time. I can't watch it anymore. Im fucking sobbing. We've been trying for months to find her a home without a dog and everything has fallen through. I posted on a group on Facebook and got absolutely torn to shreds like I was a shit person for trying to make the best decision for her. She doesnt want to go anywhere. She cries and Barks every time my wife and I leave the house. I can't put her back in the pound. I can't let her think we dont love her.