Personally, I think stashing guns about the backyard is a bit dicey, but to each his own.

Myself, I have my main supplies in the basement, a BOB in the car and another BOB in a disused car that occupies the driveway. Since theres no way it will be stolen, we leave it unlocked so you can seek shelter in it if you forgot your keys or what have you. The bag goes in the trunk and is accesible from the backseat. It seems like an odd system, but it came in handy last year when my bro got home early from a trip without his keys. I would highly reccomend that you store an out of hose kit in a car or a shed. If you go with the shed, why not organize and clean it so it can be used for shelter and storage for things other than the lawn mower and that broken week whacker you keep meaning to fix.