Using back button focus question

I am using the back button on my 7d to focus my question is what do you set the shutter release button to when using the back button to focus ?

I believe you set the shutter release button to initiate the exposure meter. Then of course to actually activate the shutter.

You have three options on the shutter button:
Metering & AF Start
Metering Start
AE lock

Since your purpose is to disconnect the AF from the shutter button, the first option is bad.

I have mine on "metering start" which turns on the meter. I suspect most back-button AF shooters set theirs up that way.

The third option, AE lock will lock your exposure to whatever it sets to when you press it. I can see where it would be useful but I personally find it awkward, especially since there is already a dedicated AE lock button on the back anyways.

my shutter button starts metering.

Metering start (that also starts IS on lenses that have it... and both also start when you press the back button).

Most folks won't want AE Lock all the time.

Another vote for meter (without lock) on the shutter button.