Stern Grove has a huge dog run (about 2 football fields). It's in a valley enclosed by trees & houses rather than fencing creating a beautiful, natural & safe setting. A determined dog may find a way out through winding paths but most would rather stay & play. Bostons in particular are all about fun & kisses so running off on their own isn't that likely. That said, all you need to be prepared for is playing with dogs & getting dirty.