Those who practice Zion birth denounce medicine, in other words if something goes wrong they pray instead of go to the hospital. Also I think it is common with Zion birth to have a midwife there, but I don't know exactly what role she plays (whether it is direct guidance or just praying.) So Zion birth is medically unassisted but unassisted birth is NOT necessarily Zion birth; in fact I'd say that the majority of unassisted births are not Zion births. In my experience, most people planning an unassisted birth plan to get medical help if they need it, and also, the vast majority of unassisted births are either solo or with only close family and/or friends present.
For my second birth I had a midwife and her assistant present for the last two hours of the labor (and for a few hours after.) The midwife's involvement was: telling me when it was safe to get int the tub, checking heart tones a couple of times, suggesting getting into a squat to push, helping bring the baby up out of the water onto my stomach, and worrying a little when the placenta didn't come right away.
I was not coached, my dilation was not checked, contractions were not timed, I was not told when to push, and I caught the baby myself. Compared to the amount of involvement midwives usually have, I think most people would consider that birth practically unassisted. However, I was looking to the midwife to safeguard the situation and therefore was alert to whatever advice she might have, and that of course interfered with my ability to go within and listen to my body. The other thing that interfered was simply her presence. I was self-conscious, both host and performer. So regardless of what degree of "assisted" or "unassisted" we want to call it, it was not unhindered.
I know that if I asked this same midwife to attend me again, she would wait on the porch or in another room until/if I needed her, and I have heard stories of other midwives doing the same, or to just check heart tones at agreed-upon times, or whatever. Would that be "unassisted"? Well, everybody defines it differently, so I can't say, nor do I personally care. What I *do* think important to figure out is whether any particular action of the midwife, or her presence alone, will adversely affect the labor and postpartum.
If you think not, then you don't have a problem, right?, and you can humor your husband by hiring a midwife. But you already know that, and you are still talking about how you would like to have an unassisted birth, so you must have your reasons for thinking it best. I'd suggest introducing it to your husband slowly -- don't even mention the word "unassisted"!, but instead get him used to the reasoning that supports it. I read to my husband passages from articles by Sarah Buckley on the chemistry of birth, articles and books by Michel Odent (a physician who goes into some detail about why observed births malfunction), Emergency Childbirth by Gregory White (another doctor who has a refreshingly relaxed attitude about birth), Lynn Griesemer, Marilyn Moran, Laura Shanley, etc., and I showed him videos of attended and unattended homebirths while pointing out the differences. We also discussed what I didn't like about my previous births and what I wanted for the next one. It wasn't long before he made the connection between what ideal, safe birth is/needs, and what we needed to do to allow it to be that.
(edited for spelling errors. Ack!)