Placing border inside of div and not on its edge

I have a <div> element and I want to put a border on it. I know I can write style="border: 1px solid black", but this adds 2px to either side of the div, which is not what I want.

I would rather have this border be -1px from the edge of the div. The div itself is 100px x 100px, and if I add a border, then I have to do some mathematics to make the border appear.

Is there any way that I can make the border appear, and ensure the box will still be 100px (including the border)?

You can also use box-shadow like this:

div{
    -webkit-box-shadow:inset 0px 0px 0px 10px #f00;
    -moz-box-shadow:inset 0px 0px 0px 10px #f00;
    box-shadow:inset 0px 0px 0px 10px #f00;
}

Example here: http://jsfiddle.net/nVyXS/ (hover to view border)

This works in modern browsers only. For example: No IE 8 support.
See caniuse.com (box-shadow feature) for more info.