As the others have mentioned, typical leases run a year here. You can find two year leases, but I wouldn't mess with them as you said the job "should" last two years. Although military members are allowed the potential to break their leases in Texas with the proper paperwork supplied by the military, it's best not to put yourself in that situation. Plus, what happens when you don't like the place or the landlord (or something similar) - you're stuck in a two year lease. At least with a one year, you'll have the potential to leave if necessary and most landlords will want to re-lease it to you again if you've been good tenants.
Are you planning on moving your license down here? We're much different from Michigan and we've been performing much better than many parts of the country. Something you might want to consider when you get here (or even before as you could do a lot of the prep work and necessary classes before you get here).
What sort of price range are you thinking of for your lease? There's a lot of areas that are considered close to Fort Sam Houston, so depending on your price range, you can go several different areas.
Hope that helps and welcome to San Antonio!
Matt Stigliano, RealtorÂ®
"Your all access pass to San Antonio real estate."