I actually used the bottom of a Lego just like it was a stamp, and used a ruler to keep the lines somewhat straight. I did notice, though, that some Legos have a circle in the middle of the base, so it's important to flip it over and make sure you're not going to get a dot in the center of your bricks. Had to discard one Lego and choose another because of this (but at least I noticed it before I started stamping). I just got the Ruby Red today and it is the perfect color for bricks. Wish I'd ordered that one much sooner!
When you follow the sheep, you end up in sheep dip.