Where are you attaching your pen tab to your Surface Pro 3?

Have you had any issue with it falling off?  I thought about doing the exact same thing, because this seems the natural place for the pen to go.

Thanks!

No problems yet, I'm kind of surprised at how well it holds.  I think the kickstand helps a lot when its closed.  If I do it again, I will cut less off so it sticks out a bit more.  That way it wouldn't be so tight in the dock with the pen attached.

Ive put mine in a similar place on the right near the charging port.

(this wouldn't be any good if you have a dock though - the normal connector is fine).

Prior to this I just stuck it on the back of the stand - which was a good place - but it soon peeled off and also meant the pen stuck out at an angle when propping up.

I think under the stand like is a brilliant place and agree that folding the stand down sort of protects it a bit from being peeled off taking in and out of bags and cases.

when you use it as a tablet

I put it in my pocket. Like I have always done.

The very Best spot to put the loop is on the left side just above the hinge on the kickstand back.  The glue won't hold the loop to the back of the keyboard very well, but it works really well on metal!  Your pen will always be next to the laptop whether or not you bring the keyboard.  This I have found works best.  Though if you're right handed, you could try it on the right, but it might block the USB port and display port.

It attaches to the power slot. Also, you do not need to detach the keyboard, just flip it over to the back of the tablet. Key presses will be ignored in this mode.