Zodi, I do understand your perspective of wanting your dog to maybe be a bit more aloof or stranger wary. I would be inclined to encourage you to discuss your alternatives with a good local trainer. Given your dogs nature, i could imagine driven to hard you may do nothing more than break her spirit, however with clever training, you may very well be able to give strangers the appearance of stranger waryness and aloofness, without it really being the case, and still hang on to the friendly young lady that you have now.
I have often heard of people simply putting studded collars on their dogs just to give an appearance of toughness too, from some reports, this has been a good first visual deterrent, or using a soft muzzle when out and about walking to also give the visiual appearance of "not so friendly"
You can teach a dog to bark on command, to the point of only needing a small hand or even wink of an eye response. This may very well be an alternative training for you. (right now i wish i could send a longer video to show you how we have trained our dog to bark on command)
We did it really for the sake of asking a simple maths question, and then Kato responding with x number of barks, it took a bit to get started but once he started to get the idea it became easier from there.
I would have a treat in my hand ready to go, and would bark at him at the same time using a signal with my hand that i wanted him to learn to recognise for one bark, the first time he barked on my hand signal, (which i will be honest was by coincence, but he still barked) he got alot of praise, the next few times a little quicker than the first, but still a little unsure. But it didnt take too long for him to recognise the hand signal as a request for him to bark.
We are now training it a little further by reducing the movement so it can be barely seen by anyone watching but only by Kato focussing on the slight movement of my hand.
Just a thought for you anyway. | 
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