My dog Cheyenne, a petite Siberian Husky at 50lbs, ended up having both hind legs done. The first one I think she was around 4 y.o. I noticed she was favoring it and took her to the vet right away. He yanked and pulled on her and told me that she was out of shape and to take her for more walks. (I walked her twice everyday except when I noticed she had a limp) So, I took her out for one that night and she tore it completely out. I carried her the whole way home. It happened right before x-mas and the surgery was around $500. I did the first choice you mentioned. Yes, she ended up loosening up the second leg one year later (also as a x-mas gift) because she favored the one leg for a long time. She lived to be 11y.o. and toward the very end, had some arthritis in the knees and hips. But, who doesn't at 77y.o.?

In the end, it's your dog and you will know what is best for him. Good luck.