Why can't I get a hard border when I used modify -> border? This is maddening and I've read about 5 posts so far that do not solve the problem?
Modify > Border command always centers the value and always anti-aliases the selection.
If you input a 4px border, you get 2 pixels inside the document and 2 pixels outside the document. PLUS 2px of anti-aliasing inside the document and 2px of anti-aliasing outside the document. So basically you get the value you input inside the document edges, but half the value is used for anti-aliasing. That's simply how the command works.
If you fill the border selection with a solid color, you see half the value in anti-aliasing. So, in the sample 4px border, you get a 2px selection inside the document, then 2px of anti-aliasing.
Repeatedly filling the selection will eventually result in a hard-edged border by filling those 2px of anti-aliasing space.
Why does this happen? I have no idea. There's certainly no way to alter the behavior of the Border command.