Not copper because you're worried about theft?

This should be an easy plumbing job, but you need to figure out what you are going to do to protect the pipes during freezing weather. A better explanation of how you intend to use this and how you will get water to it is needed f you want better advice.

Do you have a pool then who ever did the pool should have knowledge of the requirements for an outdoor shower . It will need to have the lines blown just like your sprinkler system so why do you need this is the question. Waht do you mean by rustic> I have no clue as to why not copper