Restrict Users From Changing Their Own Calendars or Alert Someone When They Do

I have a client who is looking for a solution for scheduling their techs in the field. The techs have notebooks and would be loggin in from hotels or customer sites. I was thinking that Exchange would be a perfect application for this, but they have one requirement I don't know how to meet:
One person in the office is responsible for scheduling the techs, but the techs can sometimes run into an issue where they have to stay at a site longer than originally scheduled. They don't want the techs to be able to overbook themselves or mess up the schedule.
I can think of three ways to accomplish this:
1. Don't allow the techs to change their own calendars: This would require them to inform the dispatcher when they needed something changed.
2. Allow the techs to change their own calendars, but disallow them from putting two things on the calendar at the same time. (This would be problematic as you sometimes need to have two calendar items overlapping.)
3. Allow the techs to change their calendars, but automatically send an alert to the dispatcher when they do.

I think option 3 is best, but I don't know how to accomplish any of these in Exchange. There is probably another way to avoid conflicts that I haven't thought of yet. Or maybe there is another product out there that does exactly what we need.

Can anyone help me out?