I use the corner of the bottom of the bat. Never did it any other way. I usually take guard on leg, then later on when I'm set I'll keep that guard but stand a couple of inches away so I have room to free my arms.
When I started I had an issue with showing my leg stump too much and being bowled around my legs. I find that a leg stump guard fixes that, but it brings my off stump awareness into question.
I always find that it's easier for me to see what I've done with the bat, no matter what other people have done. And since I play backyard cricket most times, there's never an umpire so I just follow the leg stump up to the popping crease and make my guard there.