How lock/pin desktop icons once they are arranged?

Hiya, does anybody know of a way (in Windows 7) to lock/pin the desktop icons in place once

you have arranged them?

My desktop isn't exactly cluttered, I think, there are at any given moment some 45-50. For

the sake of easy navigation I try to keep the number to a minimum.
 
When I have moved the icons around so that they are grouped into categories (roughly)

and have their fixed places, it's easy to find what I'm looking for, and one gets used to it,

like the layout of ones apartment for example. The desktop 'feels like home' to put it

simply, plus it looks good.

But every once in a while upon boot they are moved to the left side of the screen, not

sorted alphabetically (which, at least, would have been some help) but in completely

random order so it takes unnecessarily long to find what youre looking for.

I would understand it, and accept it, if it ocurred only after I, say, change the resolution,

but it happens randomly, 'unprovoked'.
Not a big problem, true, but kind of a drag, so if anybody knows how to pin/lock the icons

in place I'd be very grateful to know how.

Thank you!

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Hard work pays off in the future, laziness pays off now.