Hi JenT -
I didn't have any ideas for you on this, so I checked in with the rest of the OpenRoad.TV crew, and Doug McConnell offered up the following advice for you...
"Dogs off leash are always a challenge.... but a general good tip locally is that Marin County Open Space lands allow dogs off-leash on fire roads. I particularly like Blithdale ridge which can be accessed from Mill Valley and Larkspur.
There are some very nice walks over here for families and dogs with spectacular views of Mt. Tam, the city, Sausalito and the Bay.
A fun thing to do near Lafayette is to go to Tilden Park to ride the miniature railroad. Dogs are allowed on the trains. Very fun with little children and the gentle wind tickling the dogs' noses."