What version(s) of the OS and of Photoshop, before and now?
Stolen from somewhere else, here's how:
You can configure CMD + H using Edit> Keyboard Shortcuts... In that dialog, go to View> Extras and set the CMD + H kbsc, or View> Show> Selection Edges for just the marching ants and not other visible guides.
10.10.1 and cs6. Everything remained the same, but I updated from maverick to yosemite
I went to the dialog to view and extras. under extras>it already had cmd+H...what's the KBSC about. It wouldn't let me type anything additional
"CS6" is not an EXACT version of Photoshop CS6.
On the Mac, make sure you are at CS6 version 13.0.6.
kbsc = keyboard shortcut (that's what I get for copy/pasting other's advice )
Anyway, you want cmd H to hide your Selection Edges or "marching ants"
Let's explain by screenshot
Click here and you will get this white box. Inside the white box press "cmd h" on your keyboard.
The new shortcut will show up with a warning. Click the "accept" button, click OK.
Let me know how it turns out.