Self managing property from out of town-who has keys?

[Cara Fazio]

I am going to be moving out of state and plan to continue self managing my duplex.  For those who self manage from out of town:

How do you deal with simple repairs or maintenance things that need to be done?  I have someone lined up that will have a full set of keys to the property and will be the designated "in case of emergency" contact and I also have a few on call handymen, an HVAC guy, a plumber and an electrician.  However, I don't want to make the emergency contact come out to the house to grant access for small repairs or maintenance items when her only role in being there would be to open the door.

My initial thought was to install a smart lock box in a discrete location where I would be able to give out one time codes (so code would no longer work after job was complete), but I'm not sure the tenants would like the fact that there were keys to their house in a lockbox outside.  Is it reasonable to ask my tenants to be available to grant access for small things? I wouldn't expect them to take time off work or anything, just to let me know some times that work for them so that I can schedule at a time that would be convenient.  Obviously, I would have emergency person handle anything major. Tenants are all very responsible 30 something young professionals.

Would love to hear how other out-of-town self managers handle their basic maintenance requests.