I sometimes get bits of baccy and herb go in my mouth when I take a hit. Theres an easy way to solve this - get a piece of card thats about 1cm long, and roughly the same width as the roach. Then fold it together so you have something that looks like this terrible drawing -
/\/\/\/\
Squish it together and shove it up the roach so it looks like a couple of 'M's together, and that stops any bits from going in your mouth.