Well living in San Fran you are bound to be able to do what my vet suggested for Bella!!
He suggested walking upHILL (know for a fact you can find one or two in SF Hee hee). he said it will strengthen the anatomy around the knee...tighten it up so it doesnt slip! Bella no longer has an issue (knock on wood)
She also spends some time in the pool.
Also keeping good weight control will take pressure off the joints.
I keep Bella lean. Vet said you should be able to feel the ribs but not see them. Good luck with your baby!!