It's a hard choice but you're doing the right thing, my dad's dog went the same way 15 years ago, got to the point he couldn't stand up before he'd let him go but it should have been a week sooner
You'll remember the good times you had after a while, still makes me laugh when I think about Sam , there were some playing fields with a corn field beside them, he used to take off so I'd hide in the field, then I'd hear him coming , thud thud thud, he never failed to find me