Im making the switch from pencil liner (which I think is okay) to powder liner with a brush. Ive tried several times and have only had okay liner a few times. If I mess up its in every tiny crack doesnt want to come out at all.

Im using bare escentuals liner and their flat eye liner brush.

Maybe get another flat brush and when it gets out of line, dab the brush in eye makeup remover. Dab it again with a tissue to make sure it doesn't drip, and sweep it over the parts you don't want the liner. I use a thick (good brand) dark eye shadow instead of liner, but it works the same. I use a very small brush, and go over where i want the liner twice. Sometimes i use those brushes you get from sample lipsticks. They don't last that long but they're spectacular.