Due to my 13 year old daughter's unrelenting pressure, we now have a dog. Sierra arrived two months ago, and is now 4 months old. A pure bred Australian shepherd, Sierra is an athletic dog who, even at her young age, has no problem hiking several miles with over 1,000 foot elevation gains and relatively steep (40%) descents.
Although she wears a small pack, she is too young to carry any weight. The empty pack prepares her for the larger pack she will wear once her bones mature. Since she only wears the pack on the hiking trails, it also sends her the message that this is a special experience and she needs to take my commands seriously. Already, when I yell "stop!" she stops immediately and looks at me for further direction. This will come in handy if she ever approaches a rattler or a skunk while off leash. She will stay on leash, of course , until she is no longer a puppy.
Fortunately, both O'Neill Park and the Trabuco area of the Cleveland National Forest allow dogs. Caspers Park does not, except for the extreme northern portion of the park (Bell View Trail) in the Robinson Ranch area. Dogs must be leashed in the county parks (e.g. O'Neill) but not in the national forest. Obviously, dogs should only be off-leash if under voice command of their owner.