
Or a Norwegian buhund (A general farming dog, but still quite inderendat), Norwegian Elkhound (biased here as my breed, can be off lead with trainign and choosing the right places), (Keeshond (much fluffier, but least likely to be a problem off lead).
Shiba's are lovely dogs, but in common with other Asiatic Spitz are rather different to theri northern cousins, more in common with the Akita and the Chow. Also they may be small but are primitive and dog dominant generally to their own sex, and real escape artists.
All Spitz breeds (and all dogs in my opinion) need a dog proof enclosed garden.