Chain slipping off a non geared bike I have a normal ranger bike without gears, I've had this bike for quite a while now, been 8 years. But recently it's chain has started slipping off. I have maintained it well, changed the chain a couple of times and got new tyres twice. 

What could be the reason of the chain slipping? I always tell my bike guy to fix it permanently, on which he bluntly says, "there ain't a permanent fix". I ride it to work everyday so I can't afford these intermittent slip offs. Recently I went to a new repair shop where he told me I should get the rear wheel axle changed. Could it be the axle or the hub?
Is there any way to find out. Coz everytime I go to the guy complaining that the chain is slipping off, he just aligns the wheel and says it won't happen now. LOL 

I have used SO for a lot of other queries related to other walks of life. Hoping for a positive response.
So, chains aren't very different from tires in the sense that, they have to be replaced regularly, especially when you are commuting regularly. During summer and fall when I commute and race the most it's not unusual for me to replace my chain every other month. Chains get worn out, they stretch, they start to skip and behave poorly. If you haven't replaced that chain in two years, I'll bet my hat that it's falling off because it needs a replacement.

A new axle couldn't hurt either if you're axle is looking worn and starting to slip. You might have to trust the word of the repairman that pointed out the worn axle.