I just put a new belt on a 660 Rhino that had 15,000 miles on it.. And it was in first replacement belt..mind you this guy did a TON of trail riding and he wore out the drive shaft splines before the belt..
He changed all his oil every 1000 miles, he would get 3000 miles on a set of tires..
Keep the belt out of the mud and water and regualur servicing!
I am the servicing tech for a company that has over 200 rhinos, and all are over 4000km and i have never taken a belt cover off one of them to replace the belt.. now i have rebuild motors and a crap load of head gasket replacements! but no belts!